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 $202.29   8.541%   $219.5676   $219.57   $219.55   $219.60  
  Purchase #2 $22.79   8.622%   $24.755   $24.76   $24.75   $24.80  
  Purchase #3 $221.55   5.472%   $233.6732   $233.67   $233.65   $233.70  
  Purchase #4 $59.39   11.730%   $66.3564   $66.36   $66.35   $66.40  
  Purchase #5 $77.98   8.171%   $84.3517   $84.35   $84.35   $84.40  
  Purchase #6 $115.58   10.258%   $127.4362   $127.44   $127.45   $127.40  
  Purchase #7 $175.78   8.305%   $190.3785   $190.38   $190.40   $190.40  
  7 purchase totals = $875.36       $946.5186   $946.53   $946.50   $946.70