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 $72.40   4.757%   $75.8441   $75.84   $75.85   $75.80  
  Purchase #2 $22.35   11.335%   $24.8834   $24.88   $24.90   $24.90  
  Purchase #3 $87.38   6.773%   $93.2982   $93.30   $93.30   $93.30  
  Purchase #4 $88.53   10.227%   $97.584   $97.58   $97.60   $97.60  
  Purchase #5 $250.45   6.868%   $267.6509   $267.65   $267.65   $267.70  
  Purchase #6 $123.92   3.766%   $128.5868   $128.59   $128.60   $128.60  
  Purchase #7 $124.30   5.176%   $130.7338   $130.73   $130.75   $130.70  
  7 purchase totals = $769.33       $818.5812   $818.57   $818.65   $818.60