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	$24.68	8.749%	$26.8393	$26.84	$26.85	$26.80
Purchase #2	$229.40	4.318%	$239.3055	$239.31	$239.30	$239.30
Purchase #3	$61.46	7.448%	$66.0375	$66.04	$66.05	$66.00
Purchase #4	$230.92	10.653%	$255.5199	$255.52	$255.50	$255.50
Purchase #5	$34.55	3.799%	$35.8626	$35.86	$35.85	$35.90
Purchase #6	$137.50	6.779%	$146.8211	$146.82	$146.80	$146.80
Purchase #7	$151.31	7.606%	$162.8186	$162.82	$162.80	$162.80
7 purchase totals =	$869.82		$933.2045	$933.21	$933.15	$933.10