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 $115.95   8.103%   $125.3454   $125.35   $125.35   $125.30  
  Purchase #2 $188.41   11.227%   $209.5628   $209.56   $209.55   $209.60  
  Purchase #3 $234.53   8.494%   $254.451   $254.45   $254.45   $254.50  
  Purchase #4 $58.70   12.817%   $66.2236   $66.22   $66.20   $66.20  
  Purchase #5 $217.35   8.701%   $236.2616   $236.26   $236.25   $236.30  
  Purchase #6 $164.66   3.285%   $170.0691   $170.07   $170.05   $170.10  
  Purchase #7 $128.55   7.492%   $138.181   $138.18   $138.20   $138.20  
  7 purchase totals = $1,108.15       $1,200.0945   $1,200.09   $1,200.05   $1,200.20