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	$123.88	13.277%	$140.3275	$140.33	$140.35	$140.30
Purchase #2	$107.45	5.453%	$113.3092	$113.31	$113.30	$113.30
Purchase #3	$29.84	8.215%	$32.2914	$32.29	$32.30	$32.30
Purchase #4	$149.27	4.153%	$155.4692	$155.47	$155.45	$155.50
Purchase #5	$137.32	6.265%	$145.9231	$145.92	$145.90	$145.90
Purchase #6	$142.60	9.265%	$155.8119	$155.81	$155.80	$155.80
Purchase #7	$39.87	4.401%	$41.6247	$41.62	$41.60	$41.60
7 purchase totals =	$730.23		$784.7570	$784.75	$784.70	$784.70