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 $83.26   10.437%   $91.9498   $91.95   $91.95   $91.90  
  Purchase #2 $170.63   4.629%   $178.5285   $178.53   $178.55   $178.50  
  Purchase #3 $9.56   5.228%   $10.0598   $10.06   $10.05   $10.10  
  Purchase #4 $195.75   8.520%   $212.4279   $212.43   $212.45   $212.40  
  Purchase #5 $17.98   13.772%   $20.4562   $20.46   $20.45   $20.50  
  Purchase #6 $177.32   9.365%   $193.926   $193.93   $193.95   $193.90  
  Purchase #7 $190.74   7.694%   $205.4155   $205.42   $205.40   $205.40  
  7 purchase totals = $845.24       $912.7637   $912.78   $912.80   $912.70