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	$85.49	3.389%	$88.3873	$88.39	$88.40	$88.40
Purchase #2	$164.27	13.420%	$186.315	$186.32	$186.30	$186.30
Purchase #3	$94.89	5.620%	$100.2228	$100.22	$100.20	$100.20
Purchase #4	$83.87	5.645%	$88.6045	$88.60	$88.60	$88.60
Purchase #5	$33.53	6.222%	$35.6162	$35.62	$35.60	$35.60
Purchase #6	$216.42	11.428%	$241.1525	$241.15	$241.15	$241.20
Purchase #7	$107.71	9.120%	$117.5332	$117.53	$117.55	$117.50
7 purchase totals =	$786.18		$857.8315	$857.83	$857.80	$857.80