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	$9.50	8.793%	$10.3353	$10.34	$10.35	$10.30
Purchase #2	$211.49	8.322%	$229.0902	$229.09	$229.10	$229.10
Purchase #3	$40.61	4.446%	$42.4155	$42.42	$42.40	$42.40
Purchase #4	$37.29	13.795%	$42.4342	$42.43	$42.45	$42.40
Purchase #5	$169.39	12.518%	$190.5942	$190.59	$190.60	$190.60
Purchase #6	$229.44	6.757%	$244.9433	$244.94	$244.95	$244.90
Purchase #7	$64.27	12.203%	$72.1129	$72.11	$72.10	$72.10
7 purchase totals =	$761.99		$831.9256	$831.92	$831.95	$831.80