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	$211.73	10.227%	$233.3836	$233.38	$233.40	$233.40
Purchase #2	$121.83	8.404%	$132.0686	$132.07	$132.05	$132.10
Purchase #3	$82.69	8.704%	$89.8873	$89.89	$89.90	$89.90
Purchase #4	$121.99	5.295%	$128.4494	$128.45	$128.45	$128.40
Purchase #5	$116.48	7.219%	$124.8887	$124.89	$124.90	$124.90
Purchase #6	$11.83	9.810%	$12.9905	$12.99	$13.00	$13.00
Purchase #7	$250.70	3.153%	$258.6046	$258.60	$258.60	$258.60
7 purchase totals =	$917.25		$980.2727	$980.27	$980.30	$980.30