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	$39.74	5.497%	$41.9245	$41.92	$41.90	$41.90
Purchase #2	$182.31	4.492%	$190.4994	$190.50	$190.50	$190.50
Purchase #3	$154.42	10.353%	$170.4071	$170.41	$170.40	$170.40
Purchase #4	$144.86	4.154%	$150.8775	$150.88	$150.90	$150.90
Purchase #5	$88.58	8.862%	$96.43	$96.43	$96.45	$96.40
Purchase #6	$64.30	11.836%	$71.9105	$71.91	$71.90	$71.90
Purchase #7	$157.60	10.305%	$173.8407	$173.84	$173.85	$173.80
7 purchase totals =	$831.81		$895.8897	$895.89	$895.90	$895.80