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	$18.45	6.255%	$19.604	$19.60	$19.60	$19.60
Purchase #2	$96.42	4.729%	$100.9797	$100.98	$101.00	$101.00
Purchase #3	$54.85	8.585%	$59.5589	$59.56	$59.55	$59.60
Purchase #4	$215.61	11.693%	$240.8213	$240.82	$240.80	$240.80
Purchase #5	$19.85	9.529%	$21.7415	$21.74	$21.75	$21.70
Purchase #6	$219.84	10.652%	$243.2574	$243.26	$243.25	$243.30
Purchase #7	$122.32	4.714%	$128.0862	$128.09	$128.10	$128.10
7 purchase totals =	$747.34		$814.0490	$814.05	$814.05	$814.10