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 $146.38   3.144%   $150.9822   $150.98   $151.00   $151.00  
  Purchase #2 $29.57   11.554%   $32.9865   $32.99   $33.00   $33.00  
  Purchase #3 $210.71   11.481%   $234.9016   $234.90   $234.90   $234.90  
  Purchase #4 $152.91   11.727%   $170.8418   $170.84   $170.85   $170.80  
  Purchase #5 $105.88   11.395%   $117.945   $117.95   $117.95   $117.90  
  Purchase #6 $160.50   13.754%   $182.5752   $182.58   $182.60   $182.60  
  Purchase #7 $32.26   7.515%   $34.6843   $34.68   $34.70   $34.70  
  7 purchase totals = $838.21       $924.9166   $924.92   $925.00   $924.90