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	$59.38	12.629%	$66.8791	$66.88	$66.90	$66.90
Purchase #2	$122.88	6.828%	$131.2702	$131.27	$131.25	$131.30
Purchase #3	$90.29	5.517%	$95.2713	$95.27	$95.25	$95.30
Purchase #4	$104.97	7.840%	$113.1996	$113.20	$113.20	$113.20
Purchase #5	$20.42	11.249%	$22.717	$22.72	$22.70	$22.70
Purchase #6	$86.27	6.596%	$91.9604	$91.96	$91.95	$92.00
Purchase #7	$55.60	12.454%	$62.5244	$62.52	$62.50	$62.50
7 purchase totals =	$539.81		$583.8220	$583.82	$583.75	$583.90