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	$61.84	7.609%	$66.5454	$66.55	$66.55	$66.50
Purchase #2	$164.91	5.246%	$173.5612	$173.56	$173.55	$173.60
Purchase #3	$26.95	9.796%	$29.59	$29.59	$29.60	$29.60
Purchase #4	$230.60	10.465%	$254.7323	$254.73	$254.75	$254.70
Purchase #5	$103.37	4.337%	$107.8532	$107.85	$107.85	$107.90
Purchase #6	$24.76	11.483%	$27.6032	$27.60	$27.60	$27.60
Purchase #7	$32.88	3.111%	$33.9029	$33.90	$33.90	$33.90
7 purchase totals =	$645.31		$693.7882	$693.78	$693.80	$693.80