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 $60.26   12.302%   $67.6732   $67.67   $67.65   $67.70  
  Purchase #2 $71.54   6.747%   $76.3668   $76.37   $76.35   $76.40  
  Purchase #3 $76.82   11.327%   $85.5214   $85.52   $85.50   $85.50  
  Purchase #4 $153.48   9.333%   $167.8043   $167.80   $167.80   $167.80  
  Purchase #5 $60.97   8.184%   $65.9598   $65.96   $65.95   $66.00  
  Purchase #6 $114.38   9.151%   $124.8469   $124.85   $124.85   $124.80  
  Purchase #7 $125.95   6.237%   $133.8055   $133.81   $133.80   $133.80  
  7 purchase totals = $663.40       $721.9779   $721.98   $721.90   $722.00