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	$83.58	8.411%	$90.6099	$90.61	$90.60	$90.60
Purchase #2	$60.31	11.375%	$67.1703	$67.17	$67.15	$67.20
Purchase #3	$114.49	12.454%	$128.7486	$128.75	$128.75	$128.70
Purchase #4	$141.33	6.863%	$151.0295	$151.03	$151.05	$151.00
Purchase #5	$71.41	11.371%	$79.53	$79.53	$79.55	$79.50
Purchase #6	$141.63	3.561%	$146.6734	$146.67	$146.65	$146.70
Purchase #7	$65.84	10.743%	$72.9132	$72.91	$72.90	$72.90
7 purchase totals =	$678.59		$736.6749	$736.67	$736.65	$736.60