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	$49.59	13.657%	$56.3625	$56.36	$56.35	$56.40
Purchase #2	$19.59	3.157%	$20.2085	$20.21	$20.20	$20.20
Purchase #3	$82.29	10.649%	$91.0531	$91.05	$91.05	$91.10
Purchase #4	$142.91	10.476%	$157.8813	$157.88	$157.90	$157.90
Purchase #5	$95.34	4.278%	$99.4186	$99.42	$99.40	$99.40
Purchase #6	$97.91	3.770%	$101.6012	$101.60	$101.60	$101.60
Purchase #7	$60.55	11.275%	$67.377	$67.38	$67.40	$67.40
7 purchase totals =	$548.18		$593.9022	$593.90	$593.90	$594.00