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	$98.43	13.195%	$111.4178	$111.42	$111.40	$111.40
Purchase #2	$44.72	12.798%	$50.4433	$50.44	$50.45	$50.40
Purchase #3	$68.34	11.796%	$76.4014	$76.40	$76.40	$76.40
Purchase #4	$188.66	5.264%	$198.5911	$198.59	$198.60	$198.60
Purchase #5	$219.91	12.511%	$247.4229	$247.42	$247.40	$247.40
Purchase #6	$186.44	5.321%	$196.3605	$196.36	$196.35	$196.40
Purchase #7	$72.93	8.592%	$79.1961	$79.20	$79.20	$79.20
7 purchase totals =	$879.43		$959.8331	$959.83	$959.80	$959.80