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	$79.68	12.520%	$89.6559	$89.66	$89.65	$89.70
Purchase #2	$150.92	11.190%	$167.8079	$167.81	$167.80	$167.80
Purchase #3	$20.37	6.396%	$21.6729	$21.67	$21.65	$21.70
Purchase #4	$161.79	7.490%	$173.9081	$173.91	$173.90	$173.90
Purchase #5	$77.87	5.513%	$82.163	$82.16	$82.15	$82.20
Purchase #6	$141.53	3.760%	$146.8515	$146.85	$146.85	$146.90
Purchase #7	$52.44	3.869%	$54.4689	$54.47	$54.45	$54.50
7 purchase totals =	$684.60		$736.5282	$736.53	$736.45	$736.70