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	$131.52	3.614%	$136.2731	$136.27	$136.25	$136.30
Purchase #2	$247.26	6.320%	$262.8868	$262.89	$262.90	$262.90
Purchase #3	$153.25	9.800%	$168.2685	$168.27	$168.25	$168.30
Purchase #4	$54.85	5.227%	$57.717	$57.72	$57.70	$57.70
Purchase #5	$118.38	4.745%	$123.9971	$124.00	$124.00	$124.00
Purchase #6	$55.72	13.401%	$63.187	$63.19	$63.20	$63.20
Purchase #7	$227.59	10.255%	$250.9294	$250.93	$250.95	$250.90
7 purchase totals =	$988.57		$1,063.2589	$1,063.27	$1,063.25	$1,063.30