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	$15.66	7.184%	$16.785	$16.79	$16.80	$16.80
Purchase #2	$70.36	11.681%	$78.5788	$78.58	$78.60	$78.60
Purchase #3	$49.97	7.136%	$53.5359	$53.54	$53.55	$53.50
Purchase #4	$46.29	12.137%	$51.9082	$51.91	$51.90	$51.90
Purchase #5	$117.89	11.575%	$131.5358	$131.54	$131.55	$131.50
Purchase #6	$42.69	4.361%	$44.5517	$44.55	$44.55	$44.60
Purchase #7	$113.91	12.193%	$127.799	$127.80	$127.80	$127.80
7 purchase totals =	$456.77		$504.6944	$504.71	$504.75	$504.70