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	$92.76	7.217%	$99.4545	$99.45	$99.45	$99.50
Purchase #2	$235.81	13.667%	$268.0382	$268.04	$268.05	$268.00
Purchase #3	$110.71	6.106%	$117.47	$117.47	$117.45	$117.50
Purchase #4	$176.54	8.447%	$191.4523	$191.45	$191.45	$191.50
Purchase #5	$22.41	9.177%	$24.4666	$24.47	$24.45	$24.50
Purchase #6	$176.66	3.536%	$182.9067	$182.91	$182.90	$182.90
Purchase #7	$88.50	6.660%	$94.3941	$94.39	$94.40	$94.40
7 purchase totals =	$903.39		$978.1824	$978.18	$978.15	$978.30