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	$142.68	12.766%	$160.8945	$160.89	$160.90	$160.90
Purchase #2	$241.76	12.596%	$272.2121	$272.21	$272.20	$272.20
Purchase #3	$105.84	10.182%	$116.6166	$116.62	$116.60	$116.60
Purchase #4	$136.43	4.822%	$143.0087	$143.01	$143.00	$143.00
Purchase #5	$74.51	12.166%	$83.5749	$83.57	$83.55	$83.60
Purchase #6	$243.80	5.185%	$256.441	$256.44	$256.45	$256.40
Purchase #7	$64.37	12.500%	$72.4163	$72.42	$72.40	$72.40
7 purchase totals =	$1,009.39		$1,105.1641	$1,105.16	$1,105.10	$1,105.10