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	$81.72	9.266%	$89.2922	$89.29	$89.30	$89.30
Purchase #2	$191.31	13.646%	$217.4162	$217.42	$217.40	$217.40
Purchase #3	$188.81	11.747%	$210.9895	$210.99	$211.00	$211.00
Purchase #4	$231.85	4.443%	$242.1511	$242.15	$242.15	$242.20
Purchase #5	$83.85	8.130%	$90.667	$90.67	$90.65	$90.70
Purchase #6	$204.76	12.528%	$230.4123	$230.41	$230.40	$230.40
Purchase #7	$47.74	3.306%	$49.3183	$49.32	$49.30	$49.30
7 purchase totals =	$1,030.04		$1,130.2466	$1,130.25	$1,130.20	$1,130.30