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	$221.51	12.594%	$249.407	$249.41	$249.40	$249.40
Purchase #2	$99.60	10.603%	$110.1606	$110.16	$110.15	$110.20
Purchase #3	$59.96	6.739%	$64.0007	$64.00	$64.00	$64.00
Purchase #4	$18.46	11.692%	$20.6183	$20.62	$20.60	$20.60
Purchase #5	$172.56	5.114%	$181.3847	$181.38	$181.40	$181.40
Purchase #6	$134.35	5.804%	$142.1477	$142.15	$142.15	$142.10
Purchase #7	$138.51	7.231%	$148.5257	$148.53	$148.55	$148.50
7 purchase totals =	$844.95		$916.2447	$916.25	$916.25	$916.20