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 $209.89   11.507%   $234.042   $234.04   $234.05   $234.00  
  Purchase #2 $81.36   13.751%   $92.5478   $92.55   $92.55   $92.50  
  Purchase #3 $74.53   12.667%   $83.9707   $83.97   $83.95   $84.00  
  Purchase #4 $66.40   11.290%   $73.8966   $73.90   $73.90   $73.90  
  Purchase #5 $79.59   4.781%   $83.3952   $83.40   $83.40   $83.40  
  Purchase #6 $36.43   3.448%   $37.6861   $37.69   $37.70   $37.70  
  Purchase #7 $114.46   5.699%   $120.9831   $120.98   $121.00   $121.00  
  7 purchase totals = $662.66       $726.5215   $726.53   $726.55   $726.50