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	$210.34	3.241%	$217.1571	$217.16	$217.15	$217.20
Purchase #2	$53.47	11.420%	$59.5763	$59.58	$59.60	$59.60
Purchase #3	$142.83	10.231%	$157.4429	$157.44	$157.45	$157.40
Purchase #4	$95.92	8.631%	$104.1989	$104.20	$104.20	$104.20
Purchase #5	$130.40	4.848%	$136.7218	$136.72	$136.70	$136.70
Purchase #6	$151.56	13.444%	$171.9357	$171.94	$171.95	$171.90
Purchase #7	$135.65	8.238%	$146.8248	$146.82	$146.80	$146.80
7 purchase totals =	$920.17		$993.8575	$993.86	$993.85	$993.80