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	$111.42	7.713%	$120.0138	$120.01	$120.00	$120.00
Purchase #2	$122.80	12.110%	$137.6711	$137.67	$137.65	$137.70
Purchase #3	$123.42	5.290%	$129.9489	$129.95	$129.95	$129.90
Purchase #4	$105.46	6.106%	$111.8994	$111.90	$111.90	$111.90
Purchase #5	$79.30	5.108%	$83.3506	$83.35	$83.35	$83.40
Purchase #6	$138.40	13.269%	$156.7643	$156.76	$156.75	$156.80
Purchase #7	$87.60	12.401%	$98.4633	$98.46	$98.45	$98.50
7 purchase totals =	$768.40		$838.1114	$838.10	$838.05	$838.20