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 $126.51   8.260%   $136.9597   $136.96   $136.95   $137.00  
  Purchase #2 $214.94   5.751%   $227.3012   $227.30   $227.30   $227.30  
  Purchase #3 $73.42   3.263%   $75.8157   $75.82   $75.80   $75.80  
  Purchase #4 $42.68   13.851%   $48.5916   $48.59   $48.60   $48.60  
  Purchase #5 $125.52   3.606%   $130.0463   $130.05   $130.05   $130.00  
  Purchase #6 $236.81   10.595%   $261.9   $261.90   $261.90   $261.90  
  Purchase #7 $126.90   9.788%   $139.321   $139.32   $139.30   $139.30  
  7 purchase totals = $946.78       $1,019.9355   $1,019.94   $1,019.90   $1,019.90