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	$110.52	11.732%	$123.4862	$123.49	$123.50	$123.50
Purchase #2	$184.99	12.713%	$208.5078	$208.51	$208.50	$208.50
Purchase #3	$40.42	4.638%	$42.2947	$42.29	$42.30	$42.30
Purchase #4	$243.82	6.762%	$260.3071	$260.31	$260.30	$260.30
Purchase #5	$78.87	12.735%	$88.9141	$88.91	$88.90	$88.90
Purchase #6	$127.43	9.611%	$139.6773	$139.68	$139.70	$139.70
Purchase #7	$244.33	12.722%	$275.4137	$275.41	$275.40	$275.40
7 purchase totals =	$1,030.38		$1,138.6009	$1,138.60	$1,138.60	$1,138.60