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	$183.92	4.228%	$191.6961	$191.70	$191.70	$191.70
Purchase #2	$222.96	13.846%	$253.831	$253.83	$253.85	$253.80
Purchase #3	$194.86	13.710%	$221.5753	$221.58	$221.60	$221.60
Purchase #4	$69.37	4.585%	$72.5506	$72.55	$72.55	$72.60
Purchase #5	$20.51	4.721%	$21.4783	$21.48	$21.50	$21.50
Purchase #6	$39.85	5.606%	$42.084	$42.08	$42.10	$42.10
Purchase #7	$79.73	10.816%	$88.3536	$88.35	$88.35	$88.40
7 purchase totals =	$811.20		$891.5689	$891.57	$891.65	$891.70