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	$170.81	12.577%	$192.2928	$192.29	$192.30	$192.30
Purchase #2	$146.51	4.315%	$152.8319	$152.83	$152.85	$152.80
Purchase #3	$182.44	5.487%	$192.4505	$192.45	$192.45	$192.50
Purchase #4	$196.50	11.376%	$218.8538	$218.85	$218.85	$218.90
Purchase #5	$216.27	13.805%	$246.1261	$246.13	$246.15	$246.10
Purchase #6	$155.44	8.190%	$168.1705	$168.17	$168.15	$168.20
Purchase #7	$123.70	3.445%	$127.9615	$127.96	$127.95	$128.00
7 purchase totals =	$1,191.67		$1,298.6871	$1,298.68	$1,298.70	$1,298.80