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 $184.70   11.659%   $206.2342   $206.23   $206.25   $206.20  
  Purchase #2 $115.83   12.567%   $130.3864   $130.39   $130.40   $130.40  
  Purchase #3 $227.91   4.733%   $238.697   $238.70   $238.70   $238.70  
  Purchase #4 $64.54   5.850%   $68.3156   $68.32   $68.30   $68.30  
  Purchase #5 $123.32   5.803%   $130.4763   $130.48   $130.50   $130.50  
  Purchase #6 $91.38   3.425%   $94.5098   $94.51   $94.50   $94.50  
  Purchase #7 $243.55   6.262%   $258.8011   $258.80   $258.80   $258.80  
  7 purchase totals = $1,051.23       $1,127.4204   $1,127.43   $1,127.45   $1,127.40