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	$49.56	12.586%	$55.7976	$55.80	$55.80	$55.80
Purchase #2	$220.47	8.329%	$238.8329	$238.83	$238.85	$238.80
Purchase #3	$31.88	10.149%	$35.1155	$35.12	$35.10	$35.10
Purchase #4	$214.39	4.207%	$223.4094	$223.41	$223.40	$223.40
Purchase #5	$187.49	13.628%	$213.0411	$213.04	$213.05	$213.00
Purchase #6	$173.62	7.524%	$186.6832	$186.68	$186.70	$186.70
Purchase #7	$140.59	12.753%	$158.5194	$158.52	$158.50	$158.50
7 purchase totals =	$1,018.00		$1,111.3991	$1,111.40	$1,111.40	$1,111.30