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 $12.95   13.752%   $14.7309   $14.73   $14.75   $14.70  
  Purchase #2 $166.98   5.775%   $176.6231   $176.62   $176.60   $176.60  
  Purchase #3 $235.66   8.497%   $255.684   $255.68   $255.70   $255.70  
  Purchase #4 $89.48   7.400%   $96.1015   $96.10   $96.10   $96.10  
  Purchase #5 $96.99   5.688%   $102.5068   $102.51   $102.50   $102.50  
  Purchase #6 $67.95   3.478%   $70.3133   $70.31   $70.30   $70.30  
  Purchase #7 $87.77   6.264%   $93.2679   $93.27   $93.25   $93.30  
  7 purchase totals = $757.78       $809.2275   $809.22   $809.20   $809.20