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 $246.38   7.786%   $265.5631   $265.56   $265.55   $265.60  
  Purchase #2 $21.78   7.558%   $23.4261   $23.43   $23.45   $23.40  
  Purchase #3 $195.63   11.529%   $218.1842   $218.18   $218.20   $218.20  
  Purchase #4 $39.83   7.276%   $42.728   $42.73   $42.75   $42.70  
  Purchase #5 $170.75   11.105%   $189.7118   $189.71   $189.70   $189.70  
  Purchase #6 $51.39   6.284%   $54.6193   $54.62   $54.60   $54.60  
  Purchase #7 $217.29   10.435%   $239.9642   $239.96   $239.95   $240.00  
  7 purchase totals = $943.05       $1,034.1967   $1,034.19   $1,034.20   $1,034.20