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	$170.57	8.804%	$185.587	$185.59	$185.60	$185.60
Purchase #2	$240.36	7.280%	$257.8582	$257.86	$257.85	$257.90
Purchase #3	$65.29	11.606%	$72.8676	$72.87	$72.85	$72.90
Purchase #4	$66.89	6.539%	$71.2639	$71.26	$71.25	$71.30
Purchase #5	$123.35	3.171%	$127.2614	$127.26	$127.25	$127.30
Purchase #6	$25.81	3.304%	$26.6628	$26.66	$26.65	$26.70
Purchase #7	$130.51	10.358%	$144.0282	$144.03	$144.05	$144.00
7 purchase totals =	$822.78		$885.5291	$885.53	$885.50	$885.70