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	$37.77	12.269%	$42.404	$42.40	$42.40	$42.40
Purchase #2	$60.54	9.509%	$66.2967	$66.30	$66.30	$66.30
Purchase #3	$28.37	8.685%	$30.8339	$30.83	$30.85	$30.80
Purchase #4	$58.81	3.326%	$60.766	$60.77	$60.75	$60.80
Purchase #5	$78.81	6.195%	$83.6923	$83.69	$83.70	$83.70
Purchase #6	$203.75	12.847%	$229.9258	$229.93	$229.95	$229.90
Purchase #7	$128.33	12.186%	$143.9683	$143.97	$143.95	$144.00
7 purchase totals =	$596.38		$657.8870	$657.89	$657.90	$657.90