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 $124.48   6.389%   $132.433   $132.43   $132.45   $132.40  
  Purchase #2 $32.28   11.350%   $35.9438   $35.94   $35.95   $35.90  
  Purchase #3 $5.61   7.859%   $6.0509   $6.05   $6.05   $6.10  
  Purchase #4 $118.70   3.230%   $122.534   $122.53   $122.55   $122.50  
  Purchase #5 $156.37   11.515%   $174.376   $174.38   $174.40   $174.40  
  Purchase #6 $142.92   10.499%   $157.9252   $157.93   $157.95   $157.90  
  Purchase #7 $131.37   8.456%   $142.4786   $142.48   $142.50   $142.50  
  7 purchase totals = $711.73       $771.7415   $771.74   $771.85   $771.70