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 $66.73   13.166%   $75.5157   $75.52   $75.50   $75.50  
  Purchase #2 $136.80   4.254%   $142.6195   $142.62   $142.60   $142.60  
  Purchase #3 $35.83   5.319%   $37.7358   $37.74   $37.75   $37.70  
  Purchase #4 $49.84   8.754%   $54.203   $54.20   $54.20   $54.20  
  Purchase #5 $232.42   5.792%   $245.8818   $245.88   $245.90   $245.90  
  Purchase #6 $50.64   8.717%   $55.0543   $55.05   $55.05   $55.10  
  Purchase #7 $214.75   4.496%   $224.4052   $224.41   $224.40   $224.40  
  7 purchase totals = $787.01       $835.4153   $835.42   $835.40   $835.40