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 $229.46   5.292%   $241.603   $241.60   $241.60   $241.60  
  Purchase #2 $222.71   11.814%   $249.021   $249.02   $249.00   $249.00  
  Purchase #3 $12.49   9.484%   $13.6746   $13.67   $13.65   $13.70  
  Purchase #4 $246.76   6.561%   $262.9499   $262.95   $262.95   $262.90  
  Purchase #5 $250.95   4.146%   $261.3544   $261.35   $261.35   $261.40  
  Purchase #6 $11.82   8.150%   $12.7833   $12.78   $12.80   $12.80  
  Purchase #7 $148.81   7.214%   $159.5452   $159.55   $159.55   $159.50  
  7 purchase totals = $1,123.00       $1,200.9314   $1,200.92   $1,200.90   $1,200.90