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 $112.73   5.705%   $119.1612   $119.16   $119.15   $119.20  
  Purchase #2 $48.47   6.644%   $51.6903   $51.69   $51.70   $51.70  
  Purchase #3 $233.78   9.396%   $255.746   $255.75   $255.75   $255.70  
  Purchase #4 $58.45   3.714%   $60.6208   $60.62   $60.60   $60.60  
  Purchase #5 $17.45   3.701%   $18.0958   $18.10   $18.10   $18.10  
  Purchase #6 $87.43   13.198%   $98.969   $98.97   $98.95   $99.00  
  Purchase #7 $238.78   5.518%   $251.9559   $251.96   $251.95   $252.00  
  7 purchase totals = $797.09       $856.2390   $856.25   $856.20   $856.30