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	$239.27	13.496%	$271.5619	$271.56	$271.55	$271.60
Purchase #2	$83.78	7.687%	$90.2202	$90.22	$90.20	$90.20
Purchase #3	$211.75	13.505%	$240.3468	$240.35	$240.35	$240.30
Purchase #4	$41.82	3.862%	$43.4351	$43.44	$43.45	$43.40
Purchase #5	$90.71	11.525%	$101.1643	$101.16	$101.15	$101.20
Purchase #6	$11.72	5.745%	$12.3933	$12.39	$12.40	$12.40
Purchase #7	$28.32	10.848%	$31.3922	$31.39	$31.40	$31.40
7 purchase totals =	$707.37		$790.5138	$790.51	$790.50	$790.50