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 $205.58   13.151%   $232.6158   $232.62   $232.60   $232.60  
  Purchase #2 $209.42   10.492%   $231.3923   $231.39   $231.40   $231.40  
  Purchase #3 $195.99   11.200%   $217.9409   $217.94   $217.95   $217.90  
  Purchase #4 $85.63   13.779%   $97.429   $97.43   $97.45   $97.40  
  Purchase #5 $82.39   9.585%   $90.2871   $90.29   $90.30   $90.30  
  Purchase #6 $109.60   3.623%   $113.5708   $113.57   $113.55   $113.60  
  Purchase #7 $109.30   8.203%   $118.2659   $118.27   $118.25   $118.30  
  7 purchase totals = $997.91       $1,101.5018   $1,101.51   $1,101.50   $1,101.50