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 $226.25   5.159%   $237.9222   $237.92   $237.90   $237.90  
  Purchase #2 $52.71   11.558%   $58.8022   $58.80   $58.80   $58.80  
  Purchase #3 $67.95   11.447%   $75.7282   $75.73   $75.75   $75.70  
  Purchase #4 $46.35   11.275%   $51.576   $51.58   $51.60   $51.60  
  Purchase #5 $91.51   6.222%   $97.2038   $97.20   $97.20   $97.20  
  Purchase #6 $183.87   11.589%   $205.1787   $205.18   $205.20   $205.20  
  Purchase #7 $190.68   11.525%   $212.6559   $212.66   $212.65   $212.70  
  7 purchase totals = $859.32       $939.0670   $939.07   $939.10   $939.10