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	$138.60	5.717%	$146.5238	$146.52	$146.50	$146.50
Purchase #2	$193.59	3.771%	$200.8903	$200.89	$200.90	$200.90
Purchase #3	$136.64	6.607%	$145.6678	$145.67	$145.65	$145.70
Purchase #4	$116.63	6.538%	$124.2553	$124.26	$124.25	$124.30
Purchase #5	$38.52	9.743%	$42.273	$42.27	$42.25	$42.30
Purchase #6	$105.77	11.210%	$117.6268	$117.63	$117.65	$117.60
Purchase #7	$85.63	4.221%	$89.2444	$89.24	$89.25	$89.20
7 purchase totals =	$815.38		$866.4814	$866.48	$866.45	$866.50