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 $196.27   10.614%   $217.1021   $217.10   $217.10   $217.10  
  Purchase #2 $17.93   4.545%   $18.7449   $18.74   $18.75   $18.70  
  Purchase #3 $231.72   3.835%   $240.6065   $240.61   $240.60   $240.60  
  Purchase #4 $22.65   8.299%   $24.5297   $24.53   $24.55   $24.50  
  Purchase #5 $90.68   9.107%   $98.9382   $98.94   $98.95   $98.90  
  Purchase #6 $210.80   4.318%   $219.9023   $219.90   $219.90   $219.90  
  Purchase #7 $196.40   4.193%   $204.6351   $204.64   $204.65   $204.60  
  7 purchase totals = $966.45       $1,024.4588   $1,024.46   $1,024.50   $1,024.30