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 $222.94   10.674%   $246.7366   $246.74   $246.75   $246.70  
  Purchase #2 $61.96   10.677%   $68.5755   $68.58   $68.60   $68.60  
  Purchase #3 $108.73   7.193%   $116.5509   $116.55   $116.55   $116.60  
  Purchase #4 $75.77   10.823%   $83.9706   $83.97   $83.95   $84.00  
  Purchase #5 $237.89   13.713%   $270.5119   $270.51   $270.50   $270.50  
  Purchase #6 $229.86   13.775%   $261.5232   $261.52   $261.50   $261.50  
  Purchase #7 $204.36   5.636%   $215.8777   $215.88   $215.90   $215.90  
  7 purchase totals = $1,141.51       $1,263.7464   $1,263.75   $1,263.75   $1,263.80