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	$140.26	8.650%	$152.3925	$152.39	$152.40	$152.40
Purchase #2	$129.64	7.700%	$139.6223	$139.62	$139.60	$139.60
Purchase #3	$37.46	5.594%	$39.5555	$39.56	$39.55	$39.60
Purchase #4	$37.46	9.248%	$40.9243	$40.92	$40.90	$40.90
Purchase #5	$22.43	7.460%	$24.1033	$24.10	$24.10	$24.10
Purchase #6	$33.91	10.112%	$37.339	$37.34	$37.35	$37.30
Purchase #7	$190.48	10.642%	$210.7509	$210.75	$210.75	$210.80
7 purchase totals =	$591.64		$644.6878	$644.68	$644.65	$644.70