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	$151.61	11.310%	$168.7571	$168.76	$168.75	$168.80
Purchase #2	$243.42	7.124%	$260.7612	$260.76	$260.75	$260.80
Purchase #3	$152.80	8.141%	$165.2394	$165.24	$165.25	$165.20
Purchase #4	$249.53	10.481%	$275.6832	$275.68	$275.70	$275.70
Purchase #5	$74.68	4.791%	$78.2579	$78.26	$78.25	$78.30
Purchase #6	$239.92	13.468%	$272.2324	$272.23	$272.25	$272.20
Purchase #7	$98.51	13.364%	$111.6749	$111.67	$111.65	$111.70
7 purchase totals =	$1,210.47		$1,332.6061	$1,332.60	$1,332.60	$1,332.70