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	$230.52	4.512%	$240.9211	$240.92	$240.90	$240.90
Purchase #2	$20.39	7.257%	$21.8697	$21.87	$21.85	$21.90
Purchase #3	$188.92	10.780%	$209.2856	$209.29	$209.30	$209.30
Purchase #4	$31.60	5.191%	$33.2404	$33.24	$33.25	$33.20
Purchase #5	$89.92	8.773%	$97.8087	$97.81	$97.80	$97.80
Purchase #6	$126.37	3.292%	$130.5301	$130.53	$130.55	$130.50
Purchase #7	$57.56	13.865%	$65.5407	$65.54	$65.55	$65.50
7 purchase totals =	$745.28		$799.1963	$799.20	$799.20	$799.10