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 $246.63   6.125%   $261.7361   $261.74   $261.75   $261.70  
  Purchase #2 $62.84   11.163%   $69.8548   $69.85   $69.85   $69.90  
  Purchase #3 $30.60   6.570%   $32.6104   $32.61   $32.60   $32.60  
  Purchase #4 $82.49   13.323%   $93.4801   $93.48   $93.50   $93.50  
  Purchase #5 $24.60   4.716%   $25.7601   $25.76   $25.75   $25.80  
  Purchase #6 $238.25   7.327%   $255.7066   $255.71   $255.70   $255.70  
  Purchase #7 $245.84   12.847%   $277.4231   $277.42   $277.40   $277.40  
  7 purchase totals = $931.25       $1,016.5712   $1,016.57   $1,016.55   $1,016.60