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 $90.47   3.308%   $93.4627   $93.46   $93.45   $93.50  
  Purchase #2 $25.37   4.589%   $26.5342   $26.53   $26.55   $26.50  
  Purchase #3 $33.29   8.475%   $36.1113   $36.11   $36.10   $36.10  
  Purchase #4 $242.42   7.746%   $261.1979   $261.20   $261.20   $261.20  
  Purchase #5 $236.36   11.530%   $263.6123   $263.61   $263.60   $263.60  
  Purchase #6 $56.50   7.799%   $60.9064   $60.91   $60.90   $60.90  
  Purchase #7 $247.73   10.798%   $274.4799   $274.48   $274.50   $274.50  
  7 purchase totals = $932.14       $1,016.3047   $1,016.30   $1,016.30   $1,016.30