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	$231.40	12.422%	$260.1445	$260.14	$260.15	$260.10
Purchase #2	$28.81	12.770%	$32.489	$32.49	$32.50	$32.50
Purchase #3	$159.53	10.779%	$176.7257	$176.73	$176.75	$176.70
Purchase #4	$65.90	6.574%	$70.2323	$70.23	$70.25	$70.20
Purchase #5	$78.46	10.667%	$86.8293	$86.83	$86.85	$86.80
Purchase #6	$44.96	10.753%	$49.7945	$49.79	$49.80	$49.80
Purchase #7	$161.40	7.113%	$172.8804	$172.88	$172.90	$172.90
7 purchase totals =	$770.46		$849.0957	$849.09	$849.20	$849.00