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	$227.73	9.322%	$248.959	$248.96	$248.95	$249.00
Purchase #2	$99.97	11.379%	$111.3456	$111.35	$111.35	$111.30
Purchase #3	$133.96	12.489%	$150.6903	$150.69	$150.70	$150.70
Purchase #4	$83.61	5.621%	$88.3097	$88.31	$88.30	$88.30
Purchase #5	$214.59	3.509%	$222.12	$222.12	$222.10	$222.10
Purchase #6	$236.72	5.616%	$250.0142	$250.01	$250.00	$250.00
Purchase #7	$58.43	13.616%	$66.3858	$66.39	$66.40	$66.40
7 purchase totals =	$1,055.01		$1,137.8246	$1,137.83	$1,137.80	$1,137.80