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	$10.63	12.524%	$11.9613	$11.96	$11.95	$12.00
Purchase #2	$200.73	11.183%	$223.1776	$223.18	$223.20	$223.20
Purchase #3	$166.30	6.195%	$176.6023	$176.60	$176.60	$176.60
Purchase #4	$221.44	4.259%	$230.8711	$230.87	$230.85	$230.90
Purchase #5	$87.86	13.681%	$99.8801	$99.88	$99.90	$99.90
Purchase #6	$35.86	4.486%	$37.4687	$37.47	$37.45	$37.50
Purchase #7	$93.54	13.209%	$105.8957	$105.90	$105.90	$105.90
7 purchase totals =	$816.36		$885.8568	$885.86	$885.85	$886.00