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	$14.51	11.345%	$16.1562	$16.16	$16.15	$16.20
Purchase #2	$104.39	13.358%	$118.3344	$118.33	$118.35	$118.30
Purchase #3	$106.73	8.115%	$115.3911	$115.39	$115.40	$115.40
Purchase #4	$10.94	7.786%	$11.7918	$11.79	$11.80	$11.80
Purchase #5	$73.25	7.105%	$78.4544	$78.45	$78.45	$78.50
Purchase #6	$101.74	12.197%	$114.1492	$114.15	$114.15	$114.10
Purchase #7	$93.37	7.325%	$100.2094	$100.21	$100.20	$100.20
7 purchase totals =	$504.93		$554.4865	$554.48	$554.50	$554.50