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	$64.60	9.287%	$70.5994	$70.60	$70.60	$70.60
Purchase #2	$123.59	5.248%	$130.076	$130.08	$130.10	$130.10
Purchase #3	$40.77	11.790%	$45.5768	$45.58	$45.60	$45.60
Purchase #4	$29.86	12.376%	$33.5555	$33.56	$33.55	$33.60
Purchase #5	$103.48	6.761%	$110.4763	$110.48	$110.50	$110.50
Purchase #6	$41.41	7.121%	$44.3588	$44.36	$44.35	$44.40
Purchase #7	$131.68	3.696%	$136.5469	$136.55	$136.55	$136.50
7 purchase totals =	$535.39		$571.1897	$571.21	$571.25	$571.30