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	$46.85	6.836%	$50.0527	$50.05	$50.05	$50.10
Purchase #2	$118.41	7.672%	$127.4944	$127.49	$127.50	$127.50
Purchase #3	$27.47	3.220%	$28.3545	$28.35	$28.35	$28.40
Purchase #4	$238.44	9.299%	$260.6125	$260.61	$260.60	$260.60
Purchase #5	$154.73	10.610%	$171.1469	$171.15	$171.15	$171.10
Purchase #6	$133.62	8.822%	$145.408	$145.41	$145.40	$145.40
Purchase #7	$74.53	5.252%	$78.4443	$78.44	$78.45	$78.40
7 purchase totals =	$794.05		$861.5133	$861.50	$861.50	$861.50