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	$49.80	10.793%	$55.1749	$55.17	$55.15	$55.20
Purchase #2	$183.77	6.406%	$195.5423	$195.54	$195.55	$195.50
Purchase #3	$233.51	11.198%	$259.6584	$259.66	$259.65	$259.70
Purchase #4	$210.72	11.407%	$234.7568	$234.76	$234.75	$234.80
Purchase #5	$217.88	4.282%	$227.2096	$227.21	$227.20	$227.20
Purchase #6	$249.43	12.185%	$279.823	$279.82	$279.80	$279.80
Purchase #7	$44.32	9.713%	$48.6248	$48.62	$48.60	$48.60
7 purchase totals =	$1,189.43		$1,300.7898	$1,300.78	$1,300.70	$1,300.80