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 $121.41   3.477%   $125.6314   $125.63   $125.65   $125.60  
  Purchase #2 $114.83   9.145%   $125.3312   $125.33   $125.35   $125.30  
  Purchase #3 $68.54   11.216%   $76.2274   $76.23   $76.25   $76.20  
  Purchase #4 $55.83   7.177%   $59.8369   $59.84   $59.85   $59.80  
  Purchase #5 $29.28   10.337%   $32.3067   $32.31   $32.30   $32.30  
  Purchase #6 $156.31   8.186%   $169.1055   $169.11   $169.10   $169.10  
  Purchase #7 $224.66   9.255%   $245.4523   $245.45   $245.45   $245.50  
  7 purchase totals = $770.86       $833.8914   $833.90   $833.95   $833.80