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	$69.59	12.870%	$78.5462	$78.55	$78.55	$78.50
Purchase #2	$246.69	13.419%	$279.7933	$279.79	$279.80	$279.80
Purchase #3	$148.54	8.339%	$160.9268	$160.93	$160.95	$160.90
Purchase #4	$30.93	11.747%	$34.5633	$34.56	$34.55	$34.60
Purchase #5	$117.34	11.302%	$130.6018	$130.60	$130.60	$130.60
Purchase #6	$5.31	9.784%	$5.8295	$5.83	$5.85	$5.80
Purchase #7	$27.43	13.333%	$31.0872	$31.09	$31.10	$31.10
7 purchase totals =	$645.83		$721.3481	$721.35	$721.40	$721.30