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	$28.54	6.741%	$30.4639	$30.46	$30.45	$30.50
Purchase #2	$51.93	10.753%	$57.514	$57.51	$57.50	$57.50
Purchase #3	$36.94	12.692%	$41.6284	$41.63	$41.65	$41.60
Purchase #4	$106.37	8.211%	$115.104	$115.10	$115.10	$115.10
Purchase #5	$90.68	10.316%	$100.0345	$100.03	$100.05	$100.00
Purchase #6	$36.39	10.811%	$40.3241	$40.32	$40.30	$40.30
Purchase #7	$52.39	5.594%	$55.3207	$55.32	$55.30	$55.30
7 purchase totals =	$403.24		$440.3896	$440.37	$440.35	$440.30