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 $24.43   7.621%   $26.2918   $26.29   $26.30   $26.30  
  Purchase #2 $131.91   13.564%   $149.8023   $149.80   $149.80   $149.80  
  Purchase #3 $84.50   3.266%   $87.2598   $87.26   $87.25   $87.30  
  Purchase #4 $200.86   4.752%   $210.4049   $210.40   $210.40   $210.40  
  Purchase #5 $166.85   13.563%   $189.4799   $189.48   $189.50   $189.50  
  Purchase #6 $166.79   6.315%   $177.3228   $177.32   $177.30   $177.30  
  Purchase #7 $131.57   8.284%   $142.4693   $142.47   $142.45   $142.50  
  7 purchase totals = $906.91       $983.0308   $983.02   $983.00   $983.10