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	$239.31	9.748%	$262.6379	$262.64	$262.65	$262.60
Purchase #2	$121.41	11.419%	$135.2738	$135.27	$135.25	$135.30
Purchase #3	$54.55	12.106%	$61.1538	$61.15	$61.15	$61.20
Purchase #4	$114.54	8.120%	$123.8406	$123.84	$123.85	$123.80
Purchase #5	$45.76	5.514%	$48.2832	$48.28	$48.30	$48.30
Purchase #6	$90.81	10.594%	$100.4304	$100.43	$100.45	$100.40
Purchase #7	$91.36	8.222%	$98.8716	$98.87	$98.85	$98.90
7 purchase totals =	$757.74		$830.4913	$830.48	$830.50	$830.50