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 $78.32   8.761%   $85.1816   $85.18   $85.20   $85.20  
  Purchase #2 $225.64   5.760%   $238.6369   $238.64   $238.65   $238.60  
  Purchase #3 $88.96   5.566%   $93.9115   $93.91   $93.90   $93.90  
  Purchase #4 $35.64   5.779%   $37.6996   $37.70   $37.70   $37.70  
  Purchase #5 $44.45   10.341%   $49.0466   $49.05   $49.05   $49.00  
  Purchase #6 $194.36   10.302%   $214.383   $214.38   $214.40   $214.40  
  Purchase #7 $228.43   9.311%   $249.6991   $249.70   $249.70   $249.70  
  7 purchase totals = $895.80       $968.5583   $968.56   $968.60   $968.50