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	$151.49	3.445%	$156.7088	$156.71	$156.70	$156.70
Purchase #2	$175.30	8.336%	$189.913	$189.91	$189.90	$189.90
Purchase #3	$243.59	11.344%	$271.2228	$271.22	$271.20	$271.20
Purchase #4	$20.79	5.208%	$21.8727	$21.87	$21.85	$21.90
Purchase #5	$59.96	9.106%	$65.42	$65.42	$65.40	$65.40
Purchase #6	$94.52	5.559%	$99.7744	$99.77	$99.75	$99.80
Purchase #7	$32.54	5.491%	$34.3268	$34.33	$34.35	$34.30
7 purchase totals =	$778.19		$839.2385	$839.23	$839.15	$839.20