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	$141.40	13.449%	$160.4169	$160.42	$160.40	$160.40
Purchase #2	$57.26	9.776%	$62.8577	$62.86	$62.85	$62.90
Purchase #3	$221.27	7.580%	$238.0423	$238.04	$238.05	$238.00
Purchase #4	$85.43	10.684%	$94.5573	$94.56	$94.55	$94.60
Purchase #5	$83.71	10.407%	$92.4217	$92.42	$92.40	$92.40
Purchase #6	$37.92	6.766%	$40.4857	$40.49	$40.50	$40.50
Purchase #7	$136.32	12.422%	$153.2537	$153.25	$153.25	$153.30
7 purchase totals =	$763.31		$842.0353	$842.04	$842.00	$842.10