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	$107.87	11.613%	$120.3969	$120.40	$120.40	$120.40
Purchase #2	$78.47	8.638%	$85.2482	$85.25	$85.25	$85.20
Purchase #3	$101.58	10.153%	$111.8934	$111.89	$111.90	$111.90
Purchase #4	$238.61	11.761%	$266.6729	$266.67	$266.65	$266.70
Purchase #5	$228.63	3.394%	$236.3897	$236.39	$236.40	$236.40
Purchase #6	$26.62	6.241%	$28.2814	$28.28	$28.30	$28.30
Purchase #7	$153.86	7.255%	$165.0225	$165.02	$165.00	$165.00
7 purchase totals =	$935.64		$1,013.9050	$1,013.90	$1,013.90	$1,013.90