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 $32.87   10.319%   $36.2619   $36.26   $36.25   $36.30  
  Purchase #2 $49.64   4.254%   $51.7517   $51.75   $51.75   $51.80  
  Purchase #3 $241.80   7.755%   $260.5516   $260.55   $260.55   $260.60  
  Purchase #4 $146.65   4.236%   $152.8621   $152.86   $152.85   $152.90  
  Purchase #5 $152.63   10.605%   $168.8164   $168.82   $168.80   $168.80  
  Purchase #6 $65.79   7.549%   $70.7565   $70.76   $70.75   $70.80  
  Purchase #7 $122.64   9.489%   $134.2773   $134.28   $134.30   $134.30  
  7 purchase totals = $812.02       $875.2775   $875.28   $875.25   $875.50