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	$84.72	6.478%	$90.2082	$90.21	$90.20	$90.20
Purchase #2	$15.77	10.390%	$17.4085	$17.41	$17.40	$17.40
Purchase #3	$82.62	8.432%	$89.5865	$89.59	$89.60	$89.60
Purchase #4	$213.83	12.840%	$241.2858	$241.29	$241.30	$241.30
Purchase #5	$45.33	9.246%	$49.5212	$49.52	$49.50	$49.50
Purchase #6	$5.99	9.113%	$6.5359	$6.54	$6.55	$6.50
Purchase #7	$15.47	3.142%	$15.9561	$15.96	$15.95	$16.00
7 purchase totals =	$463.73		$510.5022	$510.52	$510.50	$510.50