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	$242.92	12.151%	$272.4372	$272.44	$272.45	$272.40
Purchase #2	$100.69	11.120%	$111.8867	$111.89	$111.90	$111.90
Purchase #3	$37.36	10.222%	$41.1789	$41.18	$41.20	$41.20
Purchase #4	$71.53	8.338%	$77.4942	$77.49	$77.50	$77.50
Purchase #5	$202.83	9.283%	$221.6587	$221.66	$221.65	$221.70
Purchase #6	$140.45	8.731%	$152.7127	$152.71	$152.70	$152.70
Purchase #7	$163.28	11.327%	$181.7747	$181.77	$181.75	$181.80
7 purchase totals =	$959.06		$1,059.1431	$1,059.14	$1,059.15	$1,059.20