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	$130.30	10.288%	$143.7053	$143.71	$143.70	$143.70
Purchase #2	$76.91	12.171%	$86.2707	$86.27	$86.25	$86.30
Purchase #3	$192.53	9.690%	$211.1862	$211.19	$211.20	$211.20
Purchase #4	$220.25	3.439%	$227.8244	$227.82	$227.80	$227.80
Purchase #5	$29.77	12.435%	$33.4719	$33.47	$33.45	$33.50
Purchase #6	$114.50	3.452%	$118.4525	$118.45	$118.45	$118.50
Purchase #7	$69.52	4.690%	$72.7805	$72.78	$72.80	$72.80
7 purchase totals =	$833.78		$893.6915	$893.69	$893.65	$893.80