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	$79.71	7.273%	$85.5073	$85.51	$85.50	$85.50
Purchase #2	$116.68	13.423%	$132.342	$132.34	$132.35	$132.30
Purchase #3	$74.83	13.792%	$85.1506	$85.15	$85.15	$85.20
Purchase #4	$139.88	13.789%	$159.1681	$159.17	$159.15	$159.20
Purchase #5	$244.87	12.135%	$274.585	$274.59	$274.60	$274.60
Purchase #6	$83.80	11.800%	$93.6884	$93.69	$93.70	$93.70
Purchase #7	$31.52	13.847%	$35.8846	$35.88	$35.90	$35.90
7 purchase totals =	$771.29		$866.3260	$866.33	$866.35	$866.40