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	$29.52	4.215%	$30.7643	$30.76	$30.75	$30.80
Purchase #2	$190.92	11.274%	$212.4443	$212.44	$212.45	$212.40
Purchase #3	$72.91	6.725%	$77.8132	$77.81	$77.80	$77.80
Purchase #4	$208.96	4.271%	$217.8847	$217.88	$217.90	$217.90
Purchase #5	$173.60	11.689%	$193.8921	$193.89	$193.90	$193.90
Purchase #6	$78.85	11.813%	$88.1646	$88.16	$88.15	$88.20
Purchase #7	$98.71	13.429%	$111.9658	$111.97	$111.95	$112.00
7 purchase totals =	$853.47		$932.9290	$932.91	$932.90	$933.00