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	$31.68	13.277%	$35.8862	$35.89	$35.90	$35.90
Purchase #2	$218.30	9.472%	$238.9774	$238.98	$239.00	$239.00
Purchase #3	$113.41	12.133%	$127.17	$127.17	$127.15	$127.20
Purchase #4	$220.38	9.628%	$241.5982	$241.60	$241.60	$241.60
Purchase #5	$29.28	3.860%	$30.4102	$30.41	$30.40	$30.40
Purchase #6	$118.47	11.308%	$131.8666	$131.87	$131.85	$131.90
Purchase #7	$179.77	4.744%	$188.2983	$188.30	$188.30	$188.30
7 purchase totals =	$911.29		$994.2069	$994.22	$994.20	$994.30