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	$38.83	12.258%	$43.5898	$43.59	$43.60	$43.60
Purchase #2	$27.59	11.837%	$30.8558	$30.86	$30.85	$30.90
Purchase #3	$75.67	10.833%	$83.8673	$83.87	$83.85	$83.90
Purchase #4	$19.80	10.580%	$21.8948	$21.89	$21.90	$21.90
Purchase #5	$196.49	9.224%	$214.6142	$214.61	$214.60	$214.60
Purchase #6	$100.61	10.636%	$111.3109	$111.31	$111.30	$111.30
Purchase #7	$92.46	7.131%	$99.0533	$99.05	$99.05	$99.10
7 purchase totals =	$551.45		$605.1861	$605.18	$605.15	$605.30