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	$33.43	6.260%	$35.5227	$35.52	$35.50	$35.50
Purchase #2	$158.38	4.443%	$165.4168	$165.42	$165.40	$165.40
Purchase #3	$38.59	6.563%	$41.1227	$41.12	$41.10	$41.10
Purchase #4	$208.94	7.546%	$224.7066	$224.71	$224.70	$224.70
Purchase #5	$6.86	11.739%	$7.6653	$7.67	$7.65	$7.70
Purchase #6	$47.45	8.471%	$51.4695	$51.47	$51.45	$51.50
Purchase #7	$36.92	9.325%	$40.3628	$40.36	$40.35	$40.40
7 purchase totals =	$530.57		$566.2664	$566.27	$566.15	$566.30