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	$13.51	6.127%	$14.3378	$14.34	$14.35	$14.30
Purchase #2	$177.41	6.261%	$188.5176	$188.52	$188.50	$188.50
Purchase #3	$216.56	12.589%	$243.8227	$243.82	$243.80	$243.80
Purchase #4	$56.27	8.813%	$61.2291	$61.23	$61.25	$61.20
Purchase #5	$85.93	4.865%	$90.1105	$90.11	$90.10	$90.10
Purchase #6	$214.34	6.561%	$228.4028	$228.40	$228.40	$228.40
Purchase #7	$13.96	10.679%	$15.4508	$15.45	$15.45	$15.50
7 purchase totals =	$777.98		$841.8713	$841.87	$841.85	$841.80