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	$20.57	3.164%	$21.2208	$21.22	$21.20	$21.20
Purchase #2	$41.62	5.271%	$43.8138	$43.81	$43.80	$43.80
Purchase #3	$245.66	10.202%	$270.7222	$270.72	$270.70	$270.70
Purchase #4	$120.80	11.424%	$134.6002	$134.60	$134.60	$134.60
Purchase #5	$126.90	9.418%	$138.8514	$138.85	$138.85	$138.90
Purchase #6	$236.63	8.140%	$255.8917	$255.89	$255.90	$255.90
Purchase #7	$49.86	11.358%	$55.5231	$55.52	$55.50	$55.50
7 purchase totals =	$842.04		$920.6232	$920.61	$920.55	$920.60