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	$36.27	4.702%	$37.9754	$37.98	$38.00	$38.00
Purchase #2	$15.45	13.295%	$17.5041	$17.50	$17.50	$17.50
Purchase #3	$41.47	9.729%	$45.5046	$45.50	$45.50	$45.50
Purchase #4	$19.52	8.761%	$21.2301	$21.23	$21.25	$21.20
Purchase #5	$188.58	11.804%	$210.84	$210.84	$210.85	$210.80
Purchase #6	$63.54	5.661%	$67.137	$67.14	$67.15	$67.10
Purchase #7	$167.75	13.663%	$190.6697	$190.67	$190.65	$190.70
7 purchase totals =	$532.58		$590.8609	$590.86	$590.90	$590.80