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	$101.29	10.664%	$112.0916	$112.09	$112.10	$112.10
Purchase #2	$19.48	8.118%	$21.0614	$21.06	$21.05	$21.10
Purchase #3	$141.92	4.653%	$148.5235	$148.52	$148.50	$148.50
Purchase #4	$227.84	12.789%	$256.9785	$256.98	$257.00	$257.00
Purchase #5	$83.65	7.804%	$90.178	$90.18	$90.20	$90.20
Purchase #6	$131.54	6.226%	$139.7297	$139.73	$139.75	$139.70
Purchase #7	$192.87	7.801%	$207.9158	$207.92	$207.90	$207.90
7 purchase totals =	$898.59		$976.4785	$976.48	$976.50	$976.50