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	$93.29	12.421%	$104.8776	$104.88	$104.90	$104.90
Purchase #2	$166.64	5.479%	$175.7702	$175.77	$175.75	$175.80
Purchase #3	$189.32	11.864%	$211.7809	$211.78	$211.80	$211.80
Purchase #4	$30.27	9.630%	$33.185	$33.19	$33.20	$33.20
Purchase #5	$173.25	10.163%	$190.8574	$190.86	$190.85	$190.90
Purchase #6	$42.69	12.387%	$47.978	$47.98	$48.00	$48.00
Purchase #7	$137.40	8.401%	$148.943	$148.94	$148.95	$148.90
7 purchase totals =	$832.86		$913.3921	$913.40	$913.45	$913.50