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	$30.39	7.442%	$32.6516	$32.65	$32.65	$32.70
Purchase #2	$153.67	12.267%	$172.5207	$172.52	$172.50	$172.50
Purchase #3	$139.58	8.110%	$150.8999	$150.90	$150.90	$150.90
Purchase #4	$13.72	5.512%	$14.4762	$14.48	$14.50	$14.50
Purchase #5	$141.80	4.119%	$147.6407	$147.64	$147.65	$147.60
Purchase #6	$211.40	9.182%	$230.8107	$230.81	$230.80	$230.80
Purchase #7	$100.71	12.711%	$113.5112	$113.51	$113.50	$113.50
7 purchase totals =	$791.27		$862.5110	$862.51	$862.50	$862.50