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	$206.30	10.683%	$228.339	$228.34	$228.35	$228.30
Purchase #2	$50.78	12.364%	$57.0584	$57.06	$57.05	$57.10
Purchase #3	$109.54	8.152%	$118.4697	$118.47	$118.45	$118.50
Purchase #4	$13.90	6.834%	$14.8499	$14.85	$14.85	$14.80
Purchase #5	$136.64	11.244%	$152.0038	$152.00	$152.00	$152.00
Purchase #6	$40.59	3.554%	$42.0326	$42.03	$42.05	$42.00
Purchase #7	$21.42	12.377%	$24.0712	$24.07	$24.05	$24.10
7 purchase totals =	$579.17		$636.8246	$636.82	$636.80	$636.80