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	$250.95	9.700%	$275.2922	$275.29	$275.30	$275.30
Purchase #2	$24.72	3.104%	$25.4873	$25.49	$25.50	$25.50
Purchase #3	$84.69	9.128%	$92.4205	$92.42	$92.40	$92.40
Purchase #4	$104.29	6.417%	$110.9823	$110.98	$111.00	$111.00
Purchase #5	$151.58	5.199%	$159.4606	$159.46	$159.45	$159.50
Purchase #6	$244.80	8.327%	$265.1845	$265.18	$265.20	$265.20
Purchase #7	$146.98	6.405%	$156.3941	$156.39	$156.40	$156.40
7 purchase totals =	$1,008.01		$1,085.2215	$1,085.21	$1,085.25	$1,085.30