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	$7.62	11.485%	$8.4952	$8.50	$8.50	$8.50
Purchase #2	$157.93	9.479%	$172.9002	$172.90	$172.90	$172.90
Purchase #3	$43.84	3.816%	$45.5129	$45.51	$45.50	$45.50
Purchase #4	$53.57	11.835%	$59.91	$59.91	$59.90	$59.90
Purchase #5	$23.94	4.457%	$25.007	$25.01	$25.00	$25.00
Purchase #6	$124.70	4.375%	$130.1556	$130.16	$130.15	$130.20
Purchase #7	$19.27	10.553%	$21.3036	$21.30	$21.30	$21.30
7 purchase totals =	$430.87		$463.2845	$463.29	$463.25	$463.30