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 $76.52   13.314%   $86.7079   $86.71   $86.70   $86.70  
  Purchase #2 $91.67   8.202%   $99.1888   $99.19   $99.20   $99.20  
  Purchase #3 $182.79   5.865%   $193.5106   $193.51   $193.50   $193.50  
  Purchase #4 $49.85   3.378%   $51.5339   $51.53   $51.55   $51.50  
  Purchase #5 $154.62   13.844%   $176.0256   $176.03   $176.05   $176.00  
  Purchase #6 $6.98   9.494%   $7.6427   $7.64   $7.65   $7.60  
  Purchase #7 $190.48   5.535%   $201.0231   $201.02   $201.00   $201.00  
  7 purchase totals = $752.91       $815.6326   $815.63   $815.65   $815.50