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	$73.35	11.647%	$81.8931	$81.89	$81.90	$81.90
Purchase #2	$99.37	7.735%	$107.0563	$107.06	$107.05	$107.10
Purchase #3	$230.50	12.689%	$259.7481	$259.75	$259.75	$259.70
Purchase #4	$45.29	7.656%	$48.7574	$48.76	$48.75	$48.80
Purchase #5	$95.97	4.120%	$99.924	$99.92	$99.90	$99.90
Purchase #6	$94.71	6.487%	$100.8538	$100.85	$100.85	$100.90
Purchase #7	$172.86	10.389%	$190.8184	$190.82	$190.80	$190.80
7 purchase totals =	$812.05		$889.0511	$889.05	$889.00	$889.10