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	$83.75	6.356%	$89.0732	$89.07	$89.05	$89.10
Purchase #2	$85.38	4.143%	$88.9173	$88.92	$88.90	$88.90
Purchase #3	$6.67	11.679%	$7.449	$7.45	$7.45	$7.40
Purchase #4	$157.25	13.460%	$178.4159	$178.42	$178.40	$178.40
Purchase #5	$81.70	4.341%	$85.2466	$85.25	$85.25	$85.20
Purchase #6	$50.42	5.343%	$53.1139	$53.11	$53.10	$53.10
Purchase #7	$22.91	7.595%	$24.65	$24.65	$24.65	$24.70
7 purchase totals =	$488.08		$526.8659	$526.87	$526.80	$526.80