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	$233.45	13.307%	$264.5152	$264.52	$264.50	$264.50
Purchase #2	$57.41	10.847%	$63.6373	$63.64	$63.65	$63.60
Purchase #3	$74.94	10.117%	$82.5217	$82.52	$82.50	$82.50
Purchase #4	$166.49	8.445%	$180.5501	$180.55	$180.55	$180.60
Purchase #5	$98.85	9.128%	$107.873	$107.87	$107.85	$107.90
Purchase #6	$230.93	10.841%	$255.9651	$255.97	$255.95	$256.00
Purchase #7	$165.71	4.625%	$173.3741	$173.37	$173.35	$173.40
7 purchase totals =	$1,027.78		$1,128.4365	$1,128.44	$1,128.35	$1,128.50