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	$85.25	6.303%	$90.6233	$90.62	$90.60	$90.60
Purchase #2	$135.43	10.574%	$149.7504	$149.75	$149.75	$149.80
Purchase #3	$140.66	13.150%	$159.1568	$159.16	$159.15	$159.20
Purchase #4	$247.90	4.812%	$259.8289	$259.83	$259.85	$259.80
Purchase #5	$159.62	4.515%	$166.8268	$166.83	$166.85	$166.80
Purchase #6	$96.54	13.693%	$109.7592	$109.76	$109.75	$109.80
Purchase #7	$146.64	3.444%	$151.6903	$151.69	$151.70	$151.70
7 purchase totals =	$1,012.04		$1,087.6357	$1,087.64	$1,087.65	$1,087.70