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	$100.89	7.258%	$108.2126	$108.21	$108.20	$108.20
Purchase #2	$148.90	5.310%	$156.8066	$156.81	$156.80	$156.80
Purchase #3	$140.83	8.261%	$152.464	$152.46	$152.45	$152.50
Purchase #4	$17.89	12.196%	$20.0719	$20.07	$20.05	$20.10
Purchase #5	$148.48	13.553%	$168.6035	$168.60	$168.60	$168.60
Purchase #6	$225.99	10.467%	$249.6444	$249.64	$249.65	$249.60
Purchase #7	$109.82	11.426%	$122.368	$122.37	$122.35	$122.40
7 purchase totals =	$892.80		$978.1710	$978.16	$978.10	$978.20