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	$138.59	9.755%	$152.1095	$152.11	$152.10	$152.10
Purchase #2	$231.72	4.784%	$242.8055	$242.81	$242.80	$242.80
Purchase #3	$59.30	3.254%	$61.2296	$61.23	$61.25	$61.20
Purchase #4	$126.87	9.601%	$139.0508	$139.05	$139.05	$139.10
Purchase #5	$59.64	9.126%	$65.0827	$65.08	$65.10	$65.10
Purchase #6	$36.32	3.420%	$37.5621	$37.56	$37.55	$37.60
Purchase #7	$129.91	10.593%	$143.6714	$143.67	$143.65	$143.70
7 purchase totals =	$782.35		$841.5116	$841.51	$841.50	$841.60