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	$132.64	13.586%	$150.6605	$150.66	$150.65	$150.70
Purchase #2	$75.32	10.554%	$83.2693	$83.27	$83.25	$83.30
Purchase #3	$119.59	6.813%	$127.7377	$127.74	$127.75	$127.70
Purchase #4	$249.94	6.685%	$266.6485	$266.65	$266.65	$266.60
Purchase #5	$19.36	12.436%	$21.7676	$21.77	$21.75	$21.80
Purchase #6	$89.54	12.561%	$100.7871	$100.79	$100.80	$100.80
Purchase #7	$73.74	9.614%	$80.8294	$80.83	$80.85	$80.80
7 purchase totals =	$760.13		$831.7001	$831.71	$831.70	$831.70