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 $91.54   3.413%   $94.6643   $94.66   $94.65   $94.70  
  Purchase #2 $205.38   12.343%   $230.7301   $230.73   $230.75   $230.70  
  Purchase #3 $146.49   13.741%   $166.6192   $166.62   $166.60   $166.60  
  Purchase #4 $170.89   12.784%   $192.7366   $192.74   $192.75   $192.70  
  Purchase #5 $126.97   8.524%   $137.7929   $137.79   $137.80   $137.80  
  Purchase #6 $87.96   9.743%   $96.5299   $96.53   $96.55   $96.50  
  Purchase #7 $25.97   4.758%   $27.2057   $27.21   $27.20   $27.20  
  7 purchase totals = $855.20       $946.2787   $946.28   $946.30   $946.20