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 $104.79   13.788%   $119.2384   $119.24   $119.25   $119.20  
  Purchase #2 $147.90   9.423%   $161.8366   $161.84   $161.85   $161.80  
  Purchase #3 $207.47   3.567%   $214.8705   $214.87   $214.85   $214.90  
  Purchase #4 $124.80   9.540%   $136.7059   $136.71   $136.70   $136.70  
  Purchase #5 $37.89   11.639%   $42.3   $42.30   $42.30   $42.30  
  Purchase #6 $122.53   8.387%   $132.8066   $132.81   $132.80   $132.80  
  Purchase #7 $15.63   12.477%   $17.5802   $17.58   $17.60   $17.60  
  7 purchase totals = $761.01       $825.3382   $825.35   $825.35   $825.30