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	$138.42	3.207%	$142.8591	$142.86	$142.85	$142.90
Purchase #2	$122.37	5.624%	$129.2521	$129.25	$129.25	$129.30
Purchase #3	$176.56	11.314%	$196.536	$196.54	$196.55	$196.50
Purchase #4	$146.42	10.341%	$161.5613	$161.56	$161.55	$161.60
Purchase #5	$50.39	8.328%	$54.5865	$54.59	$54.60	$54.60
Purchase #6	$147.89	5.641%	$156.2325	$156.23	$156.25	$156.20
Purchase #7	$26.91	4.737%	$28.1847	$28.18	$28.20	$28.20
7 purchase totals =	$808.96		$869.2122	$869.21	$869.25	$869.30