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 $91.53   6.467%   $97.4492   $97.45   $97.45   $97.40  
  Purchase #2 $161.61   8.371%   $175.1384   $175.14   $175.15   $175.10  
  Purchase #3 $138.97   10.215%   $153.1658   $153.17   $153.15   $153.20  
  Purchase #4 $205.71   9.352%   $224.948   $224.95   $224.95   $224.90  
  Purchase #5 $158.37   7.568%   $170.3554   $170.36   $170.35   $170.40  
  Purchase #6 $112.37   8.462%   $121.8787   $121.88   $121.90   $121.90  
  Purchase #7 $141.60   13.460%   $160.6594   $160.66   $160.65   $160.70  
  7 purchase totals = $1,010.16       $1,103.5949   $1,103.61   $1,103.60   $1,103.60