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	$25.62	10.314%	$28.2624	$28.26	$28.25	$28.30
Purchase #2	$204.68	6.240%	$217.452	$217.45	$217.45	$217.50
Purchase #3	$52.51	13.364%	$59.5274	$59.53	$59.55	$59.50
Purchase #4	$184.98	4.739%	$193.7462	$193.75	$193.75	$193.70
Purchase #5	$149.46	7.156%	$160.1554	$160.16	$160.15	$160.20
Purchase #6	$78.90	9.491%	$86.3884	$86.39	$86.40	$86.40
Purchase #7	$31.77	5.388%	$33.4818	$33.48	$33.50	$33.50
7 purchase totals =	$727.92		$779.0136	$779.02	$779.05	$779.10