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	$62.78	6.550%	$66.8921	$66.89	$66.90	$66.90
Purchase #2	$173.85	10.700%	$192.452	$192.45	$192.45	$192.50
Purchase #3	$113.70	9.672%	$124.6971	$124.70	$124.70	$124.70
Purchase #4	$73.35	6.574%	$78.172	$78.17	$78.15	$78.20
Purchase #5	$127.25	4.540%	$133.0272	$133.03	$133.05	$133.00
Purchase #6	$185.96	7.684%	$200.2492	$200.25	$200.25	$200.20
Purchase #7	$216.60	12.818%	$244.3638	$244.36	$244.35	$244.40
7 purchase totals =	$953.49		$1,039.8534	$1,039.85	$1,039.85	$1,039.90