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	$36.86	5.113%	$38.7447	$38.74	$38.75	$38.70
Purchase #2	$178.76	9.778%	$196.2392	$196.24	$196.25	$196.20
Purchase #3	$240.37	12.827%	$271.2023	$271.20	$271.20	$271.20
Purchase #4	$139.41	7.830%	$150.3258	$150.33	$150.35	$150.30
Purchase #5	$151.96	11.618%	$169.6147	$169.61	$169.60	$169.60
Purchase #6	$37.42	3.325%	$38.6642	$38.66	$38.65	$38.70
Purchase #7	$87.67	8.362%	$95.001	$95.00	$95.00	$95.00
7 purchase totals =	$872.45		$959.7919	$959.78	$959.80	$959.70