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	$234.36	13.419%	$265.8088	$265.81	$265.80	$265.80
Purchase #2	$40.55	9.459%	$44.3856	$44.39	$44.40	$44.40
Purchase #3	$127.29	7.283%	$136.5605	$136.56	$136.55	$136.60
Purchase #4	$102.54	6.509%	$109.2143	$109.21	$109.20	$109.20
Purchase #5	$114.59	11.482%	$127.7472	$127.75	$127.75	$127.70
Purchase #6	$189.59	8.179%	$205.0966	$205.10	$205.10	$205.10
Purchase #7	$83.93	10.610%	$92.835	$92.84	$92.85	$92.80
7 purchase totals =	$892.85		$981.6480	$981.66	$981.65	$981.60