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	$132.71	8.631%	$144.1642	$144.16	$144.15	$144.20
Purchase #2	$249.91	10.602%	$276.4055	$276.41	$276.40	$276.40
Purchase #3	$250.54	12.759%	$282.5064	$282.51	$282.50	$282.50
Purchase #4	$81.79	10.491%	$90.3706	$90.37	$90.35	$90.40
Purchase #5	$121.43	10.460%	$134.1316	$134.13	$134.15	$134.10
Purchase #6	$204.25	12.237%	$229.2441	$229.24	$229.25	$229.20
Purchase #7	$53.39	11.727%	$59.651	$59.65	$59.65	$59.70
7 purchase totals =	$1,094.02		$1,216.4734	$1,216.47	$1,216.45	$1,216.50