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	$79.29	12.361%	$89.091	$89.09	$89.10	$89.10
Purchase #2	$97.25	6.372%	$103.4468	$103.45	$103.45	$103.40
Purchase #3	$41.85	8.748%	$45.511	$45.51	$45.50	$45.50
Purchase #4	$9.99	7.369%	$10.7262	$10.73	$10.75	$10.70
Purchase #5	$40.79	13.730%	$46.3905	$46.39	$46.40	$46.40
Purchase #6	$59.44	5.140%	$62.4952	$62.50	$62.50	$62.50
Purchase #7	$232.60	8.738%	$252.9246	$252.92	$252.90	$252.90
7 purchase totals =	$561.21		$610.5853	$610.59	$610.60	$610.50