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 $137.42   12.258%   $154.2649   $154.26   $154.25   $154.30  
  Purchase #2 $95.34   8.752%   $103.6842   $103.68   $103.70   $103.70  
  Purchase #3 $200.48   8.457%   $217.4346   $217.43   $217.45   $217.40  
  Purchase #4 $138.38   4.259%   $144.2736   $144.27   $144.25   $144.30  
  Purchase #5 $16.78   9.265%   $18.3347   $18.33   $18.35   $18.30  
  Purchase #6 $45.41   6.698%   $48.4516   $48.45   $48.45   $48.50  
  Purchase #7 $201.30   8.811%   $219.0365   $219.04   $219.05   $219.00  
  7 purchase totals = $835.11       $905.4801   $905.46   $905.50   $905.50