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	$80.82	12.396%	$90.8384	$90.84	$90.85	$90.80
Purchase #2	$139.74	6.605%	$148.9698	$148.97	$148.95	$149.00
Purchase #3	$129.94	5.811%	$137.4908	$137.49	$137.50	$137.50
Purchase #4	$91.55	3.255%	$94.53	$94.53	$94.55	$94.50
Purchase #5	$94.75	5.813%	$100.2578	$100.26	$100.25	$100.30
Purchase #6	$172.94	9.154%	$188.7709	$188.77	$188.75	$188.80
Purchase #7	$95.33	9.581%	$104.4636	$104.46	$104.45	$104.50
7 purchase totals =	$805.07		$865.3213	$865.32	$865.30	$865.40