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	$221.93	10.576%	$245.4013	$245.40	$245.40	$245.40
Purchase #2	$80.57	3.210%	$83.1563	$83.16	$83.15	$83.20
Purchase #3	$70.31	3.745%	$72.9431	$72.94	$72.95	$72.90
Purchase #4	$19.32	6.135%	$20.5053	$20.51	$20.50	$20.50
Purchase #5	$161.28	7.707%	$173.7098	$173.71	$173.70	$173.70
Purchase #6	$112.52	3.459%	$116.4121	$116.41	$116.40	$116.40
Purchase #7	$76.37	3.218%	$78.8276	$78.83	$78.85	$78.80
7 purchase totals =	$742.30		$790.9555	$790.96	$790.95	$790.90