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	$90.56	11.155%	$100.662	$100.66	$100.65	$100.70
Purchase #2	$204.77	10.153%	$225.5603	$225.56	$225.55	$225.60
Purchase #3	$33.38	5.836%	$35.3281	$35.33	$35.35	$35.30
Purchase #4	$108.30	5.295%	$114.0345	$114.03	$114.05	$114.00
Purchase #5	$9.43	6.657%	$10.0578	$10.06	$10.05	$10.10
Purchase #6	$6.97	11.577%	$7.7769	$7.78	$7.80	$7.80
Purchase #7	$70.36	3.454%	$72.7902	$72.79	$72.80	$72.80
7 purchase totals =	$523.77		$566.2098	$566.21	$566.25	$566.30