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	$98.85	10.685%	$109.4121	$109.41	$109.40	$109.40
Purchase #2	$175.55	8.753%	$190.9159	$190.92	$190.90	$190.90
Purchase #3	$98.89	9.699%	$108.4813	$108.48	$108.50	$108.50
Purchase #4	$129.46	13.500%	$146.9371	$146.94	$146.95	$146.90
Purchase #5	$103.30	9.333%	$112.941	$112.94	$112.95	$112.90
Purchase #6	$96.51	10.784%	$106.9176	$106.92	$106.90	$106.90
Purchase #7	$144.44	11.104%	$160.4786	$160.48	$160.50	$160.50
7 purchase totals =	$847.00		$936.0836	$936.09	$936.10	$936.00