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	$47.51	11.346%	$52.9005	$52.90	$52.90	$52.90
Purchase #2	$124.93	7.352%	$134.1149	$134.11	$134.10	$134.10
Purchase #3	$122.82	13.384%	$139.2582	$139.26	$139.25	$139.30
Purchase #4	$199.59	6.739%	$213.0404	$213.04	$213.05	$213.00
Purchase #5	$96.43	4.340%	$100.6151	$100.62	$100.60	$100.60
Purchase #6	$45.83	6.421%	$48.7727	$48.77	$48.75	$48.80
Purchase #7	$192.72	13.195%	$218.1494	$218.15	$218.15	$218.10
7 purchase totals =	$829.83		$906.8512	$906.85	$906.80	$906.80