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	$125.98	13.680%	$143.2141	$143.21	$143.20	$143.20
Purchase #2	$184.85	3.423%	$191.1774	$191.18	$191.20	$191.20
Purchase #3	$250.45	5.351%	$263.8516	$263.85	$263.85	$263.90
Purchase #4	$40.82	4.218%	$42.5418	$42.54	$42.55	$42.50
Purchase #5	$68.32	5.182%	$71.8603	$71.86	$71.85	$71.90
Purchase #6	$71.74	10.469%	$79.2505	$79.25	$79.25	$79.30
Purchase #7	$6.94	8.102%	$7.5023	$7.50	$7.50	$7.50
7 purchase totals =	$749.10		$799.3980	$799.39	$799.40	$799.50