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	$125.43	8.588%	$136.2019	$136.20	$136.20	$136.20
Purchase #2	$100.88	13.474%	$114.4726	$114.47	$114.45	$114.50
Purchase #3	$43.50	3.665%	$45.0943	$45.09	$45.10	$45.10
Purchase #4	$201.35	9.511%	$220.5004	$220.50	$220.50	$220.50
Purchase #5	$209.90	13.798%	$238.862	$238.86	$238.85	$238.90
Purchase #6	$197.46	9.325%	$215.8731	$215.87	$215.85	$215.90
Purchase #7	$27.31	7.603%	$29.3864	$29.39	$29.40	$29.40
7 purchase totals =	$905.83		$1,000.3907	$1,000.38	$1,000.35	$1,000.50