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	$179.86	6.216%	$191.0401	$191.04	$191.05	$191.00
Purchase #2	$120.72	3.286%	$124.6869	$124.69	$124.70	$124.70
Purchase #3	$160.92	8.826%	$175.1228	$175.12	$175.10	$175.10
Purchase #4	$211.42	4.758%	$221.4794	$221.48	$221.50	$221.50
Purchase #5	$34.64	8.161%	$37.467	$37.47	$37.45	$37.50
Purchase #6	$80.59	5.678%	$85.1659	$85.17	$85.15	$85.20
Purchase #7	$67.31	13.574%	$76.4467	$76.45	$76.45	$76.40
7 purchase totals =	$855.46		$911.4088	$911.42	$911.40	$911.40