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	$98.48	13.646%	$111.9186	$111.92	$111.90	$111.90
Purchase #2	$249.94	7.571%	$268.863	$268.86	$268.85	$268.90
Purchase #3	$95.72	9.600%	$104.9091	$104.91	$104.90	$104.90
Purchase #4	$16.90	11.127%	$18.7805	$18.78	$18.80	$18.80
Purchase #5	$62.82	5.677%	$66.3863	$66.39	$66.40	$66.40
Purchase #6	$140.52	7.696%	$151.3344	$151.33	$151.35	$151.30
Purchase #7	$67.41	11.462%	$75.1365	$75.14	$75.15	$75.10
7 purchase totals =	$731.79		$797.3284	$797.33	$797.35	$797.30