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	$50.52	9.701%	$55.4209	$55.42	$55.40	$55.40
Purchase #2	$135.54	10.797%	$150.1743	$150.17	$150.15	$150.20
Purchase #3	$39.37	8.841%	$42.8507	$42.85	$42.85	$42.90
Purchase #4	$132.76	10.454%	$146.6387	$146.64	$146.65	$146.60
Purchase #5	$54.52	8.670%	$59.2469	$59.25	$59.25	$59.20
Purchase #6	$106.52	13.417%	$120.8118	$120.81	$120.80	$120.80
Purchase #7	$121.88	13.654%	$138.5215	$138.52	$138.50	$138.50
7 purchase totals =	$641.11		$713.6648	$713.66	$713.60	$713.60