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 $229.61   5.733%   $242.7735   $242.77   $242.75   $242.80  
  Purchase #2 $13.53   6.835%   $14.4548   $14.45   $14.45   $14.50  
  Purchase #3 $235.55   3.817%   $244.5409   $244.54   $244.55   $244.50  
  Purchase #4 $53.52   9.494%   $58.6012   $58.60   $58.60   $58.60  
  Purchase #5 $183.96   8.560%   $199.707   $199.71   $199.70   $199.70  
  Purchase #6 $175.78   9.583%   $192.625   $192.63   $192.65   $192.60  
  Purchase #7 $177.86   10.596%   $196.706   $196.71   $196.70   $196.70  
  7 purchase totals = $1,069.81       $1,149.4084   $1,149.41   $1,149.40   $1,149.40