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	$225.44	7.439%	$242.2105	$242.21	$242.20	$242.20
Purchase #2	$140.31	4.522%	$146.6548	$146.65	$146.65	$146.70
Purchase #3	$98.37	5.344%	$103.6269	$103.63	$103.65	$103.60
Purchase #4	$9.92	10.663%	$10.9778	$10.98	$11.00	$11.00
Purchase #5	$78.29	5.384%	$82.5051	$82.51	$82.50	$82.50
Purchase #6	$27.76	3.114%	$28.6244	$28.62	$28.60	$28.60
Purchase #7	$12.61	7.130%	$13.5091	$13.51	$13.50	$13.50
7 purchase totals =	$592.70		$628.1086	$628.11	$628.10	$628.10