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 $65.26   4.758%   $68.3651   $68.37   $68.35   $68.40  
  Purchase #2 $189.97   10.734%   $210.3614   $210.36   $210.35   $210.40  
  Purchase #3 $104.89   7.472%   $112.7274   $112.73   $112.75   $112.70  
  Purchase #4 $61.27   8.262%   $66.3321   $66.33   $66.35   $66.30  
  Purchase #5 $154.71   4.860%   $162.2289   $162.23   $162.25   $162.20  
  Purchase #6 $86.63   12.677%   $97.6121   $97.61   $97.60   $97.60  
  Purchase #7 $204.95   10.569%   $226.6112   $226.61   $226.60   $226.60  
  7 purchase totals = $867.68       $944.2382   $944.24   $944.25   $944.20