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 $88.51   9.426%   $96.853   $96.85   $96.85   $96.90  
  Purchase #2 $18.80   10.671%   $20.8061   $20.81   $20.80   $20.80  
  Purchase #3 $118.71   5.228%   $124.9162   $124.92   $124.90   $124.90  
  Purchase #4 $195.99   4.200%   $204.2216   $204.22   $204.20   $204.20  
  Purchase #5 $144.57   9.116%   $157.749   $157.75   $157.75   $157.70  
  Purchase #6 $236.73   10.471%   $261.518   $261.52   $261.50   $261.50  
  Purchase #7 $116.80   13.317%   $132.3543   $132.35   $132.35   $132.40  
  7 purchase totals = $920.11       $998.4182   $998.42   $998.35   $998.40