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	$122.71	12.357%	$137.8733	$137.87	$137.85	$137.90
Purchase #2	$96.78	3.822%	$100.4789	$100.48	$100.50	$100.50
Purchase #3	$72.38	4.687%	$75.7725	$75.77	$75.75	$75.80
Purchase #4	$110.46	13.446%	$125.3125	$125.31	$125.30	$125.30
Purchase #5	$156.52	9.871%	$171.9701	$171.97	$171.95	$172.00
Purchase #6	$53.81	11.188%	$59.8303	$59.83	$59.85	$59.80
Purchase #7	$221.29	8.247%	$239.5398	$239.54	$239.55	$239.50
7 purchase totals =	$833.95		$910.7774	$910.77	$910.75	$910.80