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	$30.41	13.141%	$34.4062	$34.41	$34.40	$34.40
Purchase #2	$66.64	3.823%	$69.1876	$69.19	$69.20	$69.20
Purchase #3	$124.61	5.752%	$131.7776	$131.78	$131.80	$131.80
Purchase #4	$153.30	11.780%	$171.3587	$171.36	$171.35	$171.40
Purchase #5	$136.90	11.766%	$153.0077	$153.01	$153.00	$153.00
Purchase #6	$240.60	5.272%	$253.2844	$253.28	$253.30	$253.30
Purchase #7	$89.43	12.313%	$100.4415	$100.44	$100.45	$100.40
7 purchase totals =	$841.89		$913.4637	$913.47	$913.50	$913.50