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	$236.25	8.276%	$255.8021	$255.80	$255.80	$255.80
Purchase #2	$239.63	11.386%	$266.9143	$266.91	$266.90	$266.90
Purchase #3	$176.86	7.597%	$190.2961	$190.30	$190.30	$190.30
Purchase #4	$189.43	7.776%	$204.1601	$204.16	$204.15	$204.20
Purchase #5	$205.92	8.583%	$223.5941	$223.59	$223.60	$223.60
Purchase #6	$31.32	5.304%	$32.9812	$32.98	$33.00	$33.00
Purchase #7	$110.49	11.843%	$123.5753	$123.58	$123.60	$123.60
7 purchase totals =	$1,189.90		$1,297.3232	$1,297.32	$1,297.35	$1,297.40