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 $58.96   12.686%   $66.4397   $66.44   $66.45   $66.40  
  Purchase #2 $194.82   8.405%   $211.1946   $211.19   $211.20   $211.20  
  Purchase #3 $183.72   3.655%   $190.435   $190.44   $190.45   $190.40  
  Purchase #4 $91.76   4.391%   $95.7892   $95.79   $95.80   $95.80  
  Purchase #5 $60.97   11.772%   $68.1474   $68.15   $68.15   $68.10  
  Purchase #6 $67.91   12.308%   $76.2684   $76.27   $76.25   $76.30  
  Purchase #7 $143.33   10.820%   $158.8383   $158.84   $158.85   $158.80  
  7 purchase totals = $801.47       $867.1126   $867.12   $867.15   $867.00