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	$48.80	11.868%	$54.5916	$54.59	$54.60	$54.60
Purchase #2	$241.30	5.530%	$254.6439	$254.64	$254.65	$254.60
Purchase #3	$74.87	11.155%	$83.2217	$83.22	$83.20	$83.20
Purchase #4	$250.51	13.131%	$283.4045	$283.40	$283.40	$283.40
Purchase #5	$160.92	4.331%	$167.8894	$167.89	$167.90	$167.90
Purchase #6	$18.99	12.664%	$21.3949	$21.39	$21.40	$21.40
Purchase #7	$88.46	12.811%	$99.7926	$99.79	$99.80	$99.80
7 purchase totals =	$883.85		$964.9386	$964.92	$964.95	$964.90