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	$146.95	12.429%	$165.2144	$165.21	$165.20	$165.20
Purchase #2	$228.65	10.706%	$253.1293	$253.13	$253.15	$253.10
Purchase #3	$30.64	9.596%	$33.5802	$33.58	$33.60	$33.60
Purchase #4	$204.89	11.825%	$229.1182	$229.12	$229.10	$229.10
Purchase #5	$91.62	4.230%	$95.4955	$95.50	$95.50	$95.50
Purchase #6	$163.25	3.830%	$169.5025	$169.50	$169.50	$169.50
Purchase #7	$117.35	5.293%	$123.5613	$123.56	$123.55	$123.60
7 purchase totals =	$983.35		$1,069.6014	$1,069.60	$1,069.60	$1,069.60