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 $148.33   13.485%   $168.3323   $168.33   $168.35   $168.30  
  Purchase #2 $186.42   6.850%   $199.1898   $199.19   $199.20   $199.20  
  Purchase #3 $16.77   10.774%   $18.5768   $18.58   $18.60   $18.60  
  Purchase #4 $213.75   4.844%   $224.1041   $224.10   $224.10   $224.10  
  Purchase #5 $209.78   3.859%   $217.8754   $217.88   $217.90   $217.90  
  Purchase #6 $61.88   6.469%   $65.883   $65.88   $65.90   $65.90  
  Purchase #7 $69.75   7.828%   $75.21   $75.21   $75.20   $75.20  
  7 purchase totals = $906.68       $969.1714   $969.17   $969.25   $969.20