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	$30.86	5.332%	$32.5055	$32.51	$32.50	$32.50
Purchase #2	$145.25	5.180%	$152.774	$152.77	$152.75	$152.80
Purchase #3	$34.81	5.122%	$36.593	$36.59	$36.60	$36.60
Purchase #4	$14.48	9.454%	$15.8489	$15.85	$15.85	$15.80
Purchase #5	$102.85	9.466%	$112.5858	$112.59	$112.60	$112.60
Purchase #6	$40.30	8.210%	$43.6086	$43.61	$43.60	$43.60
Purchase #7	$84.92	4.694%	$88.9061	$88.91	$88.90	$88.90
7 purchase totals =	$453.47		$482.8219	$482.83	$482.80	$482.80