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 $20.59   4.330%   $21.4815   $21.48   $21.50   $21.50  
  Purchase #2 $209.75   13.520%   $238.1082   $238.11   $238.10   $238.10  
  Purchase #3 $239.60   4.814%   $251.1343   $251.13   $251.15   $251.10  
  Purchase #4 $62.61   12.576%   $70.4838   $70.48   $70.50   $70.50  
  Purchase #5 $178.54   12.606%   $201.0468   $201.05   $201.05   $201.00  
  Purchase #6 $46.76   13.756%   $53.1923   $53.19   $53.20   $53.20  
  Purchase #7 $8.36   13.762%   $9.5105   $9.51   $9.50   $9.50  
  7 purchase totals = $766.21       $844.9574   $844.95   $845.00   $844.90