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	$53.72	10.778%	$59.5099	$59.51	$59.50	$59.50
Purchase #2	$227.80	8.218%	$246.5206	$246.52	$246.50	$246.50
Purchase #3	$42.57	6.761%	$45.4482	$45.45	$45.45	$45.40
Purchase #4	$83.27	5.451%	$87.809	$87.81	$87.80	$87.80
Purchase #5	$124.38	3.416%	$128.6288	$128.63	$128.65	$128.60
Purchase #6	$160.51	11.858%	$179.5433	$179.54	$179.55	$179.50
Purchase #7	$80.54	9.248%	$87.9883	$87.99	$88.00	$88.00
7 purchase totals =	$772.79		$835.4481	$835.45	$835.45	$835.30