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	$53.33	7.463%	$57.31	$57.31	$57.30	$57.30
Purchase #2	$146.34	5.120%	$153.8326	$153.83	$153.85	$153.80
Purchase #3	$90.31	12.648%	$101.7324	$101.73	$101.75	$101.70
Purchase #4	$134.57	12.427%	$151.293	$151.29	$151.30	$151.30
Purchase #5	$132.83	11.285%	$147.8199	$147.82	$147.80	$147.80
Purchase #6	$239.64	12.789%	$270.2876	$270.29	$270.30	$270.30
Purchase #7	$233.87	9.369%	$255.7813	$255.78	$255.80	$255.80
7 purchase totals =	$1,030.89		$1,138.0568	$1,138.05	$1,138.10	$1,138.00