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 $233.31   12.616%   $262.7444   $262.74   $262.75   $262.70  
  Purchase #2 $48.71   5.304%   $51.2936   $51.29   $51.30   $51.30  
  Purchase #3 $224.78   10.157%   $247.6109   $247.61   $247.60   $247.60  
  Purchase #4 $71.48   3.136%   $73.7216   $73.72   $73.70   $73.70  
  Purchase #5 $124.79   6.499%   $132.9001   $132.90   $132.90   $132.90  
  Purchase #6 $129.43   5.229%   $136.1979   $136.20   $136.20   $136.20  
  Purchase #7 $87.55   12.204%   $98.2346   $98.23   $98.25   $98.20  
  7 purchase totals = $920.05       $1,002.7031   $1,002.69   $1,002.70   $1,002.60