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 $188.50   8.724%   $204.9447   $204.94   $204.95   $204.90  
  Purchase #2 $121.82   3.141%   $125.6464   $125.65   $125.65   $125.60  
  Purchase #3 $55.28   5.417%   $58.2745   $58.27   $58.25   $58.30  
  Purchase #4 $65.73   12.704%   $74.0803   $74.08   $74.10   $74.10  
  Purchase #5 $53.81   8.816%   $58.5539   $58.55   $58.55   $58.60  
  Purchase #6 $235.46   5.182%   $247.6615   $247.66   $247.65   $247.70  
  Purchase #7 $154.41   9.524%   $169.116   $169.12   $169.10   $169.10  
  7 purchase totals = $875.01       $938.2773   $938.27   $938.25   $938.30