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	$102.66	6.304%	$109.1317	$109.13	$109.15	$109.10
Purchase #2	$159.74	8.155%	$172.7668	$172.77	$172.75	$172.80
Purchase #3	$141.50	7.797%	$152.5328	$152.53	$152.55	$152.50
Purchase #4	$40.52	11.419%	$45.147	$45.15	$45.15	$45.10
Purchase #5	$34.60	7.843%	$37.3137	$37.31	$37.30	$37.30
Purchase #6	$95.49	13.432%	$108.3162	$108.32	$108.30	$108.30
Purchase #7	$146.54	8.821%	$159.4663	$159.47	$159.45	$159.50
7 purchase totals =	$721.05		$784.6745	$784.68	$784.65	$784.60