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	$75.75	3.157%	$78.1414	$78.14	$78.15	$78.10
Purchase #2	$120.28	7.182%	$128.9185	$128.92	$128.90	$128.90
Purchase #3	$196.62	11.695%	$219.6147	$219.61	$219.60	$219.60
Purchase #4	$247.55	9.724%	$271.6218	$271.62	$271.60	$271.60
Purchase #5	$165.78	4.557%	$173.3346	$173.33	$173.35	$173.30
Purchase #6	$234.65	11.632%	$261.9445	$261.94	$261.95	$261.90
Purchase #7	$20.87	3.462%	$21.5925	$21.59	$21.60	$21.60
7 purchase totals =	$1,061.50		$1,155.1680	$1,155.15	$1,155.15	$1,155.00