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	$108.47	13.809%	$123.4486	$123.45	$123.45	$123.40
Purchase #2	$227.70	11.745%	$254.4434	$254.44	$254.45	$254.40
Purchase #3	$146.71	13.301%	$166.2239	$166.22	$166.20	$166.20
Purchase #4	$100.64	7.422%	$108.1095	$108.11	$108.10	$108.10
Purchase #5	$142.42	10.539%	$157.4296	$157.43	$157.45	$157.40
Purchase #6	$57.37	13.682%	$65.2194	$65.22	$65.20	$65.20
Purchase #7	$30.76	8.183%	$33.2771	$33.28	$33.30	$33.30
7 purchase totals =	$814.07		$908.1515	$908.15	$908.15	$908.00