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	$39.74	6.724%	$42.4121	$42.41	$42.40	$42.40
Purchase #2	$70.37	7.845%	$75.8905	$75.89	$75.90	$75.90
Purchase #3	$87.49	3.674%	$90.7044	$90.70	$90.70	$90.70
Purchase #4	$110.62	3.644%	$114.651	$114.65	$114.65	$114.70
Purchase #5	$78.90	5.849%	$83.5149	$83.51	$83.50	$83.50
Purchase #6	$142.37	5.322%	$149.9469	$149.95	$149.95	$149.90
Purchase #7	$99.96	3.480%	$103.4386	$103.44	$103.45	$103.40
7 purchase totals =	$629.45		$660.5584	$660.55	$660.55	$660.50