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 $87.83   11.147%   $97.6204   $97.62   $97.60   $97.60  
  Purchase #2 $60.34   8.634%   $65.5498   $65.55   $65.55   $65.50  
  Purchase #3 $44.39   8.872%   $48.3283   $48.33   $48.35   $48.30  
  Purchase #4 $163.85   13.338%   $185.7043   $185.70   $185.70   $185.70  
  Purchase #5 $107.67   11.356%   $119.897   $119.90   $119.90   $119.90  
  Purchase #6 $136.37   13.281%   $154.4813   $154.48   $154.50   $154.50  
  Purchase #7 $237.70   13.513%   $269.8204   $269.82   $269.80   $269.80  
  7 purchase totals = $838.15       $941.4015   $941.40   $941.40   $941.30