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	$99.59	13.565%	$113.0994	$113.10	$113.10	$113.10
Purchase #2	$217.49	3.465%	$225.026	$225.03	$225.05	$225.00
Purchase #3	$33.63	6.200%	$35.7151	$35.72	$35.70	$35.70
Purchase #4	$49.90	13.209%	$56.4913	$56.49	$56.50	$56.50
Purchase #5	$143.80	6.736%	$153.4864	$153.49	$153.50	$153.50
Purchase #6	$85.83	7.664%	$92.408	$92.41	$92.40	$92.40
Purchase #7	$68.79	13.764%	$78.2583	$78.26	$78.25	$78.30
7 purchase totals =	$699.03		$754.4845	$754.50	$754.50	$754.50