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	$93.72	7.141%	$100.4125	$100.41	$100.40	$100.40
Purchase #2	$132.36	8.579%	$143.7152	$143.72	$143.70	$143.70
Purchase #3	$127.84	13.722%	$145.3822	$145.38	$145.40	$145.40
Purchase #4	$178.53	7.447%	$191.8251	$191.83	$191.85	$191.80
Purchase #5	$199.33	4.580%	$208.4593	$208.46	$208.45	$208.50
Purchase #6	$220.31	4.471%	$230.1601	$230.16	$230.15	$230.20
Purchase #7	$203.79	7.315%	$218.6972	$218.70	$218.70	$218.70
7 purchase totals =	$1,155.88		$1,238.6516	$1,238.66	$1,238.65	$1,238.70