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 $182.53   10.530%   $201.7504   $201.75   $201.75   $201.80  
  Purchase #2 $64.25   4.227%   $66.9658   $66.97   $66.95   $67.00  
  Purchase #3 $97.93   13.230%   $110.8861   $110.89   $110.90   $110.90  
  Purchase #4 $238.38   10.758%   $264.0249   $264.02   $264.00   $264.00  
  Purchase #5 $201.79   11.858%   $225.7183   $225.72   $225.70   $225.70  
  Purchase #6 $205.73   13.819%   $234.1598   $234.16   $234.15   $234.20  
  Purchase #7 $242.88   5.504%   $256.2481   $256.25   $256.25   $256.20  
  7 purchase totals = $1,233.49       $1,359.7534   $1,359.76   $1,359.70   $1,359.80