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	$61.34	6.866%	$65.5516	$65.55	$65.55	$65.60
Purchase #2	$230.85	8.512%	$250.5	$250.50	$250.50	$250.50
Purchase #3	$141.77	12.131%	$158.9681	$158.97	$158.95	$159.00
Purchase #4	$135.69	10.757%	$150.2862	$150.29	$150.30	$150.30
Purchase #5	$87.39	3.690%	$90.6147	$90.61	$90.60	$90.60
Purchase #6	$211.56	3.583%	$219.1402	$219.14	$219.15	$219.10
Purchase #7	$143.42	9.514%	$157.065	$157.07	$157.05	$157.10
7 purchase totals =	$1,012.02		$1,092.1258	$1,092.13	$1,092.10	$1,092.20