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 $23.77   6.289%   $25.2649   $25.26   $25.25   $25.30  
  Purchase #2 $157.79   12.347%   $177.2723   $177.27   $177.25   $177.30  
  Purchase #3 $150.46   5.590%   $158.8707   $158.87   $158.85   $158.90  
  Purchase #4 $162.71   13.772%   $185.1184   $185.12   $185.10   $185.10  
  Purchase #5 $121.29   4.247%   $126.4412   $126.44   $126.45   $126.40  
  Purchase #6 $104.89   5.269%   $110.4167   $110.42   $110.40   $110.40  
  Purchase #7 $218.73   9.450%   $239.4   $239.40   $239.40   $239.40  
  7 purchase totals = $939.64       $1,022.7842   $1,022.78   $1,022.70   $1,022.80