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	$247.34	4.547%	$258.5865	$258.59	$258.60	$258.60
Purchase #2	$70.25	13.128%	$79.4724	$79.47	$79.45	$79.50
Purchase #3	$245.27	9.374%	$268.2616	$268.26	$268.25	$268.30
Purchase #4	$230.61	3.413%	$238.4807	$238.48	$238.50	$238.50
Purchase #5	$250.95	9.676%	$275.2319	$275.23	$275.25	$275.20
Purchase #6	$49.50	10.654%	$54.7737	$54.77	$54.75	$54.80
Purchase #7	$247.54	13.750%	$281.5768	$281.58	$281.60	$281.60
7 purchase totals =	$1,341.46		$1,456.3836	$1,456.38	$1,456.40	$1,456.50