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	$139.93	13.775%	$159.2054	$159.21	$159.20	$159.20
Purchase #2	$157.90	9.325%	$172.6242	$172.62	$172.60	$172.60
Purchase #3	$179.56	9.212%	$196.1011	$196.10	$196.10	$196.10
Purchase #4	$103.79	13.412%	$117.7103	$117.71	$117.70	$117.70
Purchase #5	$40.28	12.585%	$45.3492	$45.35	$45.35	$45.30
Purchase #6	$217.34	11.313%	$241.9277	$241.93	$241.95	$241.90
Purchase #7	$130.63	12.398%	$146.8255	$146.83	$146.85	$146.80
7 purchase totals =	$969.43		$1,079.7434	$1,079.75	$1,079.75	$1,079.60