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	$222.30	9.457%	$243.3229	$243.32	$243.30	$243.30
Purchase #2	$88.28	4.784%	$92.5033	$92.50	$92.50	$92.50
Purchase #3	$113.73	10.852%	$126.072	$126.07	$126.05	$126.10
Purchase #4	$120.43	6.452%	$128.2001	$128.20	$128.20	$128.20
Purchase #5	$240.98	5.702%	$254.7207	$254.72	$254.70	$254.70
Purchase #6	$243.63	13.346%	$276.1449	$276.14	$276.15	$276.10
Purchase #7	$54.30	8.829%	$59.0941	$59.09	$59.10	$59.10
7 purchase totals =	$1,083.65		$1,180.0580	$1,180.04	$1,180.00	$1,180.00