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	$183.88	8.433%	$199.3866	$199.39	$199.40	$199.40
Purchase #2	$85.81	5.250%	$90.315	$90.32	$90.30	$90.30
Purchase #3	$70.65	3.791%	$73.3283	$73.33	$73.35	$73.30
Purchase #4	$95.66	8.199%	$103.5032	$103.50	$103.50	$103.50
Purchase #5	$186.38	11.840%	$208.4474	$208.45	$208.45	$208.40
Purchase #6	$237.26	13.318%	$268.8583	$268.86	$268.85	$268.90
Purchase #7	$21.81	12.645%	$24.5679	$24.57	$24.55	$24.60
7 purchase totals =	$881.45		$968.4067	$968.42	$968.40	$968.40