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 $87.84   11.125%   $97.6122   $97.61   $97.60   $97.60  
  Purchase #2 $140.79   9.107%   $153.6117   $153.61   $153.60   $153.60  
  Purchase #3 $81.94   13.264%   $92.8085   $92.81   $92.80   $92.80  
  Purchase #4 $16.25   11.208%   $18.0713   $18.07   $18.05   $18.10  
  Purchase #5 $111.34   11.720%   $124.389   $124.39   $124.40   $124.40  
  Purchase #6 $184.95   9.162%   $201.8951   $201.90   $201.90   $201.90  
  Purchase #7 $65.72   8.528%   $71.3246   $71.32   $71.30   $71.30  
  7 purchase totals = $688.83       $759.7124   $759.71   $759.65   $759.70