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	$138.91	4.179%	$144.715	$144.72	$144.70	$144.70
Purchase #2	$113.68	12.173%	$127.5183	$127.52	$127.50	$127.50
Purchase #3	$136.65	3.118%	$140.9107	$140.91	$140.90	$140.90
Purchase #4	$65.92	8.185%	$71.3156	$71.32	$71.30	$71.30
Purchase #5	$184.98	12.445%	$208.0008	$208.00	$208.00	$208.00
Purchase #6	$230.60	7.220%	$247.2493	$247.25	$247.25	$247.20
Purchase #7	$72.39	7.827%	$78.056	$78.06	$78.05	$78.10
7 purchase totals =	$943.13		$1,017.7657	$1,017.78	$1,017.70	$1,017.70