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	$123.91	10.774%	$137.2601	$137.26	$137.25	$137.30
Purchase #2	$103.33	3.350%	$106.7916	$106.79	$106.80	$106.80
Purchase #3	$183.66	8.490%	$199.2527	$199.25	$199.25	$199.30
Purchase #4	$78.27	6.786%	$83.5814	$83.58	$83.60	$83.60
Purchase #5	$112.93	3.523%	$116.9085	$116.91	$116.90	$116.90
Purchase #6	$96.66	7.449%	$103.8602	$103.86	$103.85	$103.90
Purchase #7	$71.43	13.746%	$81.2488	$81.25	$81.25	$81.20
7 purchase totals =	$770.19		$828.9033	$828.90	$828.90	$829.00