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	$209.50	8.544%	$227.3997	$227.40	$227.40	$227.40
Purchase #2	$173.73	8.253%	$188.0679	$188.07	$188.05	$188.10
Purchase #3	$54.40	9.295%	$59.4565	$59.46	$59.45	$59.50
Purchase #4	$122.68	12.378%	$137.8653	$137.87	$137.85	$137.90
Purchase #5	$80.92	13.560%	$91.8928	$91.89	$91.90	$91.90
Purchase #6	$83.72	4.771%	$87.7143	$87.71	$87.70	$87.70
Purchase #7	$45.78	3.747%	$47.4954	$47.50	$47.50	$47.50
7 purchase totals =	$770.73		$839.8919	$839.90	$839.85	$840.00