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	$48.35	8.157%	$52.2939	$52.29	$52.30	$52.30
Purchase #2	$37.63	12.385%	$42.2905	$42.29	$42.30	$42.30
Purchase #3	$134.94	3.337%	$139.4429	$139.44	$139.45	$139.40
Purchase #4	$90.93	10.328%	$100.3213	$100.32	$100.30	$100.30
Purchase #5	$85.64	8.677%	$93.071	$93.07	$93.05	$93.10
Purchase #6	$47.98	5.861%	$50.7921	$50.79	$50.80	$50.80
Purchase #7	$139.51	11.849%	$156.0405	$156.04	$156.05	$156.00
7 purchase totals =	$584.98		$634.2522	$634.24	$634.25	$634.20