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	$132.26	12.573%	$148.889	$148.89	$148.90	$148.90
Purchase #2	$141.95	3.273%	$146.596	$146.60	$146.60	$146.60
Purchase #3	$172.53	9.265%	$188.5149	$188.51	$188.50	$188.50
Purchase #4	$61.36	10.684%	$67.9157	$67.92	$67.90	$67.90
Purchase #5	$9.52	6.798%	$10.1672	$10.17	$10.15	$10.20
Purchase #6	$61.27	11.712%	$68.4459	$68.45	$68.45	$68.40
Purchase #7	$26.50	11.350%	$29.5078	$29.51	$29.50	$29.50
7 purchase totals =	$605.39		$660.0365	$660.05	$660.00	$660.00