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	$145.37	8.407%	$157.5913	$157.59	$157.60	$157.60
Purchase #2	$18.83	6.162%	$19.9903	$19.99	$20.00	$20.00
Purchase #3	$66.27	11.470%	$73.8712	$73.87	$73.85	$73.90
Purchase #4	$68.93	13.775%	$78.4251	$78.43	$78.45	$78.40
Purchase #5	$50.72	5.697%	$53.6095	$53.61	$53.60	$53.60
Purchase #6	$186.42	6.401%	$198.3527	$198.35	$198.35	$198.40
Purchase #7	$31.46	5.650%	$33.2375	$33.24	$33.25	$33.20
7 purchase totals =	$568.00		$615.0776	$615.08	$615.10	$615.10