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	$245.72	7.721%	$264.692	$264.69	$264.70	$264.70
Purchase #2	$139.35	6.696%	$148.6809	$148.68	$148.70	$148.70
Purchase #3	$49.79	4.223%	$51.8926	$51.89	$51.90	$51.90
Purchase #4	$45.70	13.388%	$51.8183	$51.82	$51.80	$51.80
Purchase #5	$223.37	13.118%	$252.6717	$252.67	$252.65	$252.70
Purchase #6	$238.48	8.555%	$258.882	$258.88	$258.90	$258.90
Purchase #7	$157.59	9.222%	$172.1229	$172.12	$172.10	$172.10
7 purchase totals =	$1,100.00		$1,200.7604	$1,200.75	$1,200.75	$1,200.80