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	$48.72	3.188%	$50.2732	$50.27	$50.25	$50.30
Purchase #2	$22.61	12.859%	$25.5174	$25.52	$25.50	$25.50
Purchase #3	$48.31	13.516%	$54.8396	$54.84	$54.85	$54.80
Purchase #4	$115.59	6.251%	$122.8155	$122.82	$122.80	$122.80
Purchase #5	$86.94	10.784%	$96.3156	$96.32	$96.30	$96.30
Purchase #6	$141.68	3.509%	$146.6516	$146.65	$146.65	$146.70
Purchase #7	$46.79	3.610%	$48.4791	$48.48	$48.50	$48.50
7 purchase totals =	$510.64		$544.8920	$544.90	$544.85	$544.90