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	$225.73	3.233%	$233.0279	$233.03	$233.05	$233.00
Purchase #2	$175.37	12.777%	$197.777	$197.78	$197.80	$197.80
Purchase #3	$130.54	11.522%	$145.5808	$145.58	$145.60	$145.60
Purchase #4	$136.54	3.560%	$141.4008	$141.40	$141.40	$141.40
Purchase #5	$34.54	7.442%	$37.1105	$37.11	$37.10	$37.10
Purchase #6	$228.75	4.795%	$239.7186	$239.72	$239.70	$239.70
Purchase #7	$130.39	5.183%	$137.1481	$137.15	$137.15	$137.10
7 purchase totals =	$1,061.86		$1,131.7637	$1,131.77	$1,131.80	$1,131.70