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 $218.89   12.402%   $246.0367   $246.04   $246.05   $246.00  
  Purchase #2 $62.62   7.290%   $67.185   $67.19   $67.20   $67.20  
  Purchase #3 $29.61   11.285%   $32.9515   $32.95   $32.95   $33.00  
  Purchase #4 $105.79   9.844%   $116.204   $116.20   $116.20   $116.20  
  Purchase #5 $59.42   12.234%   $66.6894   $66.69   $66.70   $66.70  
  Purchase #6 $146.26   5.632%   $154.4974   $154.50   $154.50   $154.50  
  Purchase #7 $182.46   3.609%   $189.045   $189.05   $189.05   $189.00  
  7 purchase totals = $805.05       $872.6090   $872.62   $872.65   $872.60