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	$48.75	12.602%	$54.8935	$54.89	$54.90	$54.90
Purchase #2	$47.90	8.662%	$52.0491	$52.05	$52.05	$52.00
Purchase #3	$35.72	7.800%	$38.5062	$38.51	$38.50	$38.50
Purchase #4	$134.57	13.449%	$152.6683	$152.67	$152.65	$152.70
Purchase #5	$220.86	12.431%	$248.3151	$248.32	$248.30	$248.30
Purchase #6	$153.98	12.738%	$173.594	$173.59	$173.60	$173.60
Purchase #7	$197.51	6.253%	$209.8603	$209.86	$209.85	$209.90
7 purchase totals =	$839.29		$929.8865	$929.89	$929.85	$929.90