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	$15.33	13.184%	$17.3511	$17.35	$17.35	$17.40
Purchase #2	$149.48	4.387%	$156.0377	$156.04	$156.05	$156.00
Purchase #3	$9.32	6.614%	$9.9364	$9.94	$9.95	$9.90
Purchase #4	$129.43	8.648%	$140.6231	$140.62	$140.60	$140.60
Purchase #5	$151.97	9.139%	$165.8585	$165.86	$165.85	$165.90
Purchase #6	$78.90	13.860%	$89.8355	$89.84	$89.85	$89.80
Purchase #7	$40.55	11.597%	$45.2526	$45.25	$45.25	$45.30
7 purchase totals =	$574.98		$624.8949	$624.90	$624.90	$624.90