Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $73.46   4.132%   $76.4954   $76.50   $76.50   $76.50  
  Purchase #2 $228.25   9.302%   $249.4818   $249.48   $249.50   $249.50  
  Purchase #3 $99.30   5.441%   $104.7029   $104.70   $104.70   $104.70  
  Purchase #4 $240.51   3.509%   $248.9495   $248.95   $248.95   $248.90  
  Purchase #5 $215.61   12.121%   $241.7441   $241.74   $241.75   $241.70  
  Purchase #6 $193.72   4.774%   $202.9682   $202.97   $202.95   $203.00  
  Purchase #7 $126.98   5.392%   $133.8268   $133.83   $133.85   $133.80  
  7 purchase totals = $1,177.83       $1,258.1687   $1,258.17   $1,258.20   $1,258.10