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	$223.90	7.735%	$241.2187	$241.22	$241.20	$241.20
Purchase #2	$47.33	6.595%	$50.4514	$50.45	$50.45	$50.50
Purchase #3	$90.60	9.473%	$99.1825	$99.18	$99.20	$99.20
Purchase #4	$98.49	11.251%	$109.5711	$109.57	$109.55	$109.60
Purchase #5	$16.91	5.719%	$17.8771	$17.88	$17.90	$17.90
Purchase #6	$39.82	4.562%	$41.6366	$41.64	$41.65	$41.60
Purchase #7	$26.39	6.646%	$28.1439	$28.14	$28.15	$28.10
7 purchase totals =	$543.44		$588.0813	$588.08	$588.10	$588.10