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 $92.88   8.659%   $100.9225   $100.92   $100.90   $100.90  
  Purchase #2 $67.72   11.248%   $75.3371   $75.34   $75.35   $75.30  
  Purchase #3 $17.28   12.554%   $19.4493   $19.45   $19.45   $19.40  
  Purchase #4 $177.31   6.784%   $189.3387   $189.34   $189.35   $189.30  
  Purchase #5 $68.29   8.804%   $74.3023   $74.30   $74.30   $74.30  
  Purchase #6 $206.64   6.766%   $220.6213   $220.62   $220.60   $220.60  
  Purchase #7 $240.57   8.623%   $261.3144   $261.31   $261.30   $261.30  
  7 purchase totals = $870.69       $941.2856   $941.28   $941.25   $941.10