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	$40.50	12.464%	$45.5479	$45.55	$45.55	$45.50
Purchase #2	$82.41	11.856%	$92.1805	$92.18	$92.20	$92.20
Purchase #3	$172.68	8.146%	$186.7465	$186.75	$186.75	$186.70
Purchase #4	$142.29	6.246%	$151.1774	$151.18	$151.20	$151.20
Purchase #5	$166.77	6.743%	$178.0153	$178.02	$178.00	$178.00
Purchase #6	$72.41	8.232%	$78.3708	$78.37	$78.35	$78.40
Purchase #7	$75.61	9.324%	$82.6599	$82.66	$82.65	$82.70
7 purchase totals =	$752.67		$814.6983	$814.71	$814.70	$814.70