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	$100.58	3.670%	$104.2713	$104.27	$104.25	$104.30
Purchase #2	$13.60	4.727%	$14.2429	$14.24	$14.25	$14.20
Purchase #3	$33.91	11.638%	$37.8564	$37.86	$37.85	$37.90
Purchase #4	$109.45	13.772%	$124.5235	$124.52	$124.50	$124.50
Purchase #5	$121.38	8.184%	$131.3137	$131.31	$131.30	$131.30
Purchase #6	$123.81	8.570%	$134.4205	$134.42	$134.40	$134.40
Purchase #7	$205.94	8.853%	$224.1719	$224.17	$224.15	$224.20
7 purchase totals =	$708.67		$770.8002	$770.79	$770.70	$770.80