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	$172.26	10.707%	$190.7039	$190.70	$190.70	$190.70
Purchase #2	$91.97	9.721%	$100.9104	$100.91	$100.90	$100.90
Purchase #3	$111.50	4.741%	$116.7862	$116.79	$116.80	$116.80
Purchase #4	$120.89	12.840%	$136.4123	$136.41	$136.40	$136.40
Purchase #5	$240.43	10.729%	$266.2257	$266.23	$266.25	$266.20
Purchase #6	$12.28	4.310%	$12.8093	$12.81	$12.80	$12.80
Purchase #7	$41.26	13.334%	$46.7616	$46.76	$46.75	$46.80
7 purchase totals =	$790.59		$870.6094	$870.61	$870.60	$870.60