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	$155.36	11.796%	$173.6863	$173.69	$173.70	$173.70
Purchase #2	$138.67	12.598%	$156.1396	$156.14	$156.15	$156.10
Purchase #3	$39.62	9.370%	$43.3324	$43.33	$43.35	$43.30
Purchase #4	$156.25	10.729%	$173.0141	$173.01	$173.00	$173.00
Purchase #5	$112.87	9.104%	$123.1457	$123.15	$123.15	$123.10
Purchase #6	$243.54	12.567%	$274.1457	$274.15	$274.15	$274.10
Purchase #7	$17.78	3.153%	$18.3406	$18.34	$18.35	$18.30
7 purchase totals =	$864.09		$961.8044	$961.81	$961.85	$961.60