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	$37.59	13.423%	$42.6357	$42.64	$42.65	$42.60
Purchase #2	$190.74	3.271%	$196.9791	$196.98	$197.00	$197.00
Purchase #3	$15.35	12.255%	$17.2311	$17.23	$17.25	$17.20
Purchase #4	$32.66	9.144%	$35.6464	$35.65	$35.65	$35.60
Purchase #5	$101.25	3.157%	$104.4465	$104.45	$104.45	$104.40
Purchase #6	$11.78	13.319%	$13.349	$13.35	$13.35	$13.30
Purchase #7	$199.44	4.356%	$208.1276	$208.13	$208.15	$208.10
7 purchase totals =	$588.81		$618.4154	$618.43	$618.50	$618.20