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	$108.39	5.705%	$114.5736	$114.57	$114.55	$114.60
Purchase #2	$250.91	8.586%	$272.4531	$272.45	$272.45	$272.50
Purchase #3	$152.93	12.584%	$172.1747	$172.17	$172.15	$172.20
Purchase #4	$136.30	6.309%	$144.8992	$144.90	$144.90	$144.90
Purchase #5	$171.78	9.374%	$187.8827	$187.88	$187.90	$187.90
Purchase #6	$235.95	5.665%	$249.3166	$249.32	$249.30	$249.30
Purchase #7	$136.64	10.831%	$151.4395	$151.44	$151.45	$151.40
7 purchase totals =	$1,192.90		$1,292.7394	$1,292.73	$1,292.70	$1,292.80