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	$171.60	13.364%	$194.5326	$194.53	$194.55	$194.50
Purchase #2	$37.78	9.267%	$41.2811	$41.28	$41.30	$41.30
Purchase #3	$139.52	7.652%	$150.1961	$150.20	$150.20	$150.20
Purchase #4	$140.56	8.184%	$152.0634	$152.06	$152.05	$152.10
Purchase #5	$149.32	11.471%	$166.4485	$166.45	$166.45	$166.40
Purchase #6	$48.66	9.427%	$53.2472	$53.25	$53.25	$53.20
Purchase #7	$38.62	10.862%	$42.8149	$42.81	$42.80	$42.80
7 purchase totals =	$726.06		$800.5838	$800.58	$800.60	$800.50