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	$95.66	4.513%	$99.9771	$99.98	$100.00	$100.00
Purchase #2	$32.45	7.822%	$34.9882	$34.99	$35.00	$35.00
Purchase #3	$17.45	13.664%	$19.8344	$19.83	$19.85	$19.80
Purchase #4	$179.47	6.679%	$191.4568	$191.46	$191.45	$191.50
Purchase #5	$233.59	9.619%	$256.059	$256.06	$256.05	$256.10
Purchase #6	$6.55	10.678%	$7.2494	$7.25	$7.25	$7.20
Purchase #7	$50.47	9.636%	$55.3333	$55.33	$55.35	$55.30
7 purchase totals =	$615.64		$664.8982	$664.90	$664.95	$664.90