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	$30.84	5.706%	$32.5997	$32.60	$32.60	$32.60
Purchase #2	$16.83	10.466%	$18.5914	$18.59	$18.60	$18.60
Purchase #3	$28.71	10.656%	$31.7693	$31.77	$31.75	$31.80
Purchase #4	$123.52	9.333%	$135.0481	$135.05	$135.05	$135.00
Purchase #5	$150.45	9.551%	$164.8195	$164.82	$164.80	$164.80
Purchase #6	$145.60	11.384%	$162.1751	$162.18	$162.20	$162.20
Purchase #7	$96.79	3.319%	$100.0025	$100.00	$100.00	$100.00
7 purchase totals =	$592.74		$645.0056	$645.01	$645.00	$645.00