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	$137.40	10.329%	$151.592	$151.59	$151.60	$151.60
Purchase #2	$92.67	10.364%	$102.2743	$102.27	$102.25	$102.30
Purchase #3	$35.60	3.122%	$36.7114	$36.71	$36.70	$36.70
Purchase #4	$205.27	11.572%	$229.0238	$229.02	$229.00	$229.00
Purchase #5	$195.34	10.624%	$216.0929	$216.09	$216.10	$216.10
Purchase #6	$86.89	11.181%	$96.6052	$96.61	$96.60	$96.60
Purchase #7	$78.47	12.540%	$88.3101	$88.31	$88.30	$88.30
7 purchase totals =	$831.64		$920.6097	$920.60	$920.55	$920.60