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 $101.95   11.805%   $113.9852   $113.99   $114.00   $114.00  
  Purchase #2 $30.49   4.791%   $31.9508   $31.95   $31.95   $32.00  
  Purchase #3 $154.39   12.306%   $173.3892   $173.39   $173.40   $173.40  
  Purchase #4 $113.44   11.218%   $126.1657   $126.17   $126.15   $126.20  
  Purchase #5 $231.94   10.650%   $256.6416   $256.64   $256.65   $256.60  
  Purchase #6 $16.63   5.457%   $17.5375   $17.54   $17.55   $17.50  
  Purchase #7 $228.67   12.521%   $257.3018   $257.30   $257.30   $257.30  
  7 purchase totals = $877.51       $976.9718   $976.98   $977.00   $977.00