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 $41.73   12.533%   $46.96   $46.96   $46.95   $47.00  
  Purchase #2 $115.88   11.187%   $128.8435   $128.84   $128.85   $128.80  
  Purchase #3 $62.99   3.227%   $65.0227   $65.02   $65.00   $65.00  
  Purchase #4 $76.36   13.445%   $86.6266   $86.63   $86.65   $86.60  
  Purchase #5 $59.87   13.529%   $67.9698   $67.97   $67.95   $68.00  
  Purchase #6 $63.91   12.153%   $71.677   $71.68   $71.70   $71.70  
  Purchase #7 $84.28   6.623%   $89.8619   $89.86   $89.85   $89.90  
  7 purchase totals = $505.02       $556.9615   $556.96   $556.95   $557.00