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	$124.72	9.428%	$136.4786	$136.48	$136.50	$136.50
Purchase #2	$158.69	8.522%	$172.2136	$172.21	$172.20	$172.20
Purchase #3	$29.52	9.193%	$32.2338	$32.23	$32.25	$32.20
Purchase #4	$189.46	10.796%	$209.9141	$209.91	$209.90	$209.90
Purchase #5	$109.61	6.375%	$116.5976	$116.60	$116.60	$116.60
Purchase #6	$230.87	9.653%	$253.1559	$253.16	$253.15	$253.20
Purchase #7	$78.56	4.387%	$82.0064	$82.01	$82.00	$82.00
7 purchase totals =	$921.43		$1,002.6000	$1,002.60	$1,002.60	$1,002.60