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	$200.72	9.574%	$219.9369	$219.94	$219.95	$219.90
Purchase #2	$37.67	3.266%	$38.9003	$38.90	$38.90	$38.90
Purchase #3	$103.54	12.707%	$116.6968	$116.70	$116.70	$116.70
Purchase #4	$248.91	12.450%	$279.8993	$279.90	$279.90	$279.90
Purchase #5	$57.33	3.232%	$59.1829	$59.18	$59.20	$59.20
Purchase #6	$43.87	4.705%	$45.9341	$45.93	$45.95	$45.90
Purchase #7	$59.98	13.801%	$68.2578	$68.26	$68.25	$68.30
7 purchase totals =	$752.02		$828.8081	$828.81	$828.85	$828.80