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	$209.42	3.322%	$216.3769	$216.38	$216.40	$216.40
Purchase #2	$145.92	4.268%	$152.1479	$152.15	$152.15	$152.10
Purchase #3	$228.75	11.726%	$255.5732	$255.57	$255.55	$255.60
Purchase #4	$128.54	13.871%	$146.3698	$146.37	$146.35	$146.40
Purchase #5	$121.67	8.179%	$131.6214	$131.62	$131.60	$131.60
Purchase #6	$129.93	12.798%	$146.5584	$146.56	$146.55	$146.60
Purchase #7	$233.67	11.499%	$260.5397	$260.54	$260.55	$260.50
7 purchase totals =	$1,197.90		$1,309.1873	$1,309.19	$1,309.15	$1,309.20