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	$102.50	13.565%	$116.4041	$116.40	$116.40	$116.40
Purchase #2	$136.92	13.854%	$155.8889	$155.89	$155.90	$155.90
Purchase #3	$69.35	10.255%	$76.4618	$76.46	$76.45	$76.50
Purchase #4	$20.92	7.764%	$22.5442	$22.54	$22.55	$22.50
Purchase #5	$119.52	8.198%	$129.3182	$129.32	$129.30	$129.30
Purchase #6	$170.76	12.772%	$192.5695	$192.57	$192.55	$192.60
Purchase #7	$104.25	6.696%	$111.2306	$111.23	$111.25	$111.20
7 purchase totals =	$724.22		$804.4173	$804.41	$804.40	$804.40