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 $26.61   8.795%   $28.9503   $28.95   $28.95   $29.00  
  Purchase #2 $176.30   7.563%   $189.6336   $189.63   $189.65   $189.60  
  Purchase #3 $143.85   7.464%   $154.587   $154.59   $154.60   $154.60  
  Purchase #4 $125.79   13.269%   $142.4811   $142.48   $142.50   $142.50  
  Purchase #5 $44.89   3.117%   $46.2892   $46.29   $46.30   $46.30  
  Purchase #6 $106.85   11.411%   $119.0427   $119.04   $119.05   $119.00  
  Purchase #7 $143.42   13.164%   $162.2998   $162.30   $162.30   $162.30  
  7 purchase totals = $767.71       $843.2837   $843.28   $843.35   $843.30