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	$121.37	11.583%	$135.4283	$135.43	$135.45	$135.40
Purchase #2	$149.34	4.714%	$156.3799	$156.38	$156.40	$156.40
Purchase #3	$83.60	6.474%	$89.0123	$89.01	$89.00	$89.00
Purchase #4	$90.36	9.619%	$99.0517	$99.05	$99.05	$99.10
Purchase #5	$235.36	7.661%	$253.3909	$253.39	$253.40	$253.40
Purchase #6	$143.51	13.236%	$162.505	$162.51	$162.50	$162.50
Purchase #7	$95.47	10.390%	$105.3893	$105.39	$105.40	$105.40
7 purchase totals =	$919.01		$1,001.1574	$1,001.16	$1,001.20	$1,001.20