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	$16.92	9.419%	$18.5137	$18.51	$18.50	$18.50
Purchase #2	$159.80	4.872%	$167.5855	$167.59	$167.60	$167.60
Purchase #3	$133.63	13.219%	$151.2945	$151.29	$151.30	$151.30
Purchase #4	$74.41	8.322%	$80.6024	$80.60	$80.60	$80.60
Purchase #5	$123.52	9.189%	$134.8703	$134.87	$134.85	$134.90
Purchase #6	$162.60	10.352%	$179.4324	$179.43	$179.45	$179.40
Purchase #7	$146.86	9.553%	$160.8895	$160.89	$160.90	$160.90
7 purchase totals =	$817.74		$893.1883	$893.18	$893.20	$893.20