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	$160.89	11.503%	$179.3972	$179.40	$179.40	$179.40
Purchase #2	$187.83	3.533%	$194.466	$194.47	$194.45	$194.50
Purchase #3	$180.62	13.437%	$204.8899	$204.89	$204.90	$204.90
Purchase #4	$92.82	11.494%	$103.4887	$103.49	$103.50	$103.50
Purchase #5	$36.36	6.485%	$38.7179	$38.72	$38.70	$38.70
Purchase #6	$30.35	11.480%	$33.8342	$33.83	$33.85	$33.80
Purchase #7	$32.69	9.867%	$35.9155	$35.92	$35.90	$35.90
7 purchase totals =	$721.56		$790.7094	$790.72	$790.70	$790.70