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	$31.42	6.627%	$33.5022	$33.50	$33.50	$33.50
Purchase #2	$131.36	6.265%	$139.5897	$139.59	$139.60	$139.60
Purchase #3	$108.27	8.417%	$117.3831	$117.38	$117.40	$117.40
Purchase #4	$69.68	5.770%	$73.7005	$73.70	$73.70	$73.70
Purchase #5	$25.48	11.836%	$28.4958	$28.50	$28.50	$28.50
Purchase #6	$29.34	10.142%	$32.3157	$32.32	$32.30	$32.30
Purchase #7	$33.72	13.173%	$38.1619	$38.16	$38.15	$38.20
7 purchase totals =	$429.27		$463.1489	$463.15	$463.15	$463.20