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	$93.35	11.855%	$104.4166	$104.42	$104.40	$104.40
Purchase #2	$55.91	5.835%	$59.1723	$59.17	$59.15	$59.20
Purchase #3	$14.41	9.554%	$15.7867	$15.79	$15.80	$15.80
Purchase #4	$37.65	8.507%	$40.8529	$40.85	$40.85	$40.90
Purchase #5	$59.92	5.281%	$63.0844	$63.08	$63.10	$63.10
Purchase #6	$46.91	9.672%	$51.4471	$51.45	$51.45	$51.40
Purchase #7	$219.33	7.521%	$235.8258	$235.83	$235.85	$235.80
7 purchase totals =	$527.48		$570.5858	$570.59	$570.60	$570.60