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 $232.51   6.620%   $247.9022   $247.90   $247.90   $247.90  
  Purchase #2 $68.45   7.508%   $73.5892   $73.59   $73.60   $73.60  
  Purchase #3 $100.45   4.873%   $105.3449   $105.34   $105.35   $105.30  
  Purchase #4 $211.37   7.538%   $227.3031   $227.30   $227.30   $227.30  
  Purchase #5 $187.50   3.696%   $194.43   $194.43   $194.45   $194.40  
  Purchase #6 $22.53   11.448%   $25.1092   $25.11   $25.10   $25.10  
  Purchase #7 $112.29   5.801%   $118.8039   $118.80   $118.80   $118.80  
  7 purchase totals = $935.10       $992.4825   $992.47   $992.50   $992.40