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	$227.60	6.638%	$242.7081	$242.71	$242.70	$242.70
Purchase #2	$145.76	13.297%	$165.1417	$165.14	$165.15	$165.10
Purchase #3	$242.61	10.530%	$268.1568	$268.16	$268.15	$268.20
Purchase #4	$69.72	3.624%	$72.2467	$72.25	$72.25	$72.20
Purchase #5	$97.43	6.539%	$103.8009	$103.80	$103.80	$103.80
Purchase #6	$67.25	5.612%	$71.0241	$71.02	$71.00	$71.00
Purchase #7	$103.92	3.534%	$107.5925	$107.59	$107.60	$107.60
7 purchase totals =	$954.29		$1,030.6708	$1,030.67	$1,030.65	$1,030.60