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	$171.56	8.373%	$185.9247	$185.92	$185.90	$185.90
Purchase #2	$220.89	11.636%	$246.5928	$246.59	$246.60	$246.60
Purchase #3	$225.80	9.116%	$246.3839	$246.38	$246.40	$246.40
Purchase #4	$78.94	3.643%	$81.8158	$81.82	$81.80	$81.80
Purchase #5	$29.71	9.118%	$32.419	$32.42	$32.40	$32.40
Purchase #6	$38.45	4.791%	$40.2921	$40.29	$40.30	$40.30
Purchase #7	$40.33	13.510%	$45.7786	$45.78	$45.80	$45.80
7 purchase totals =	$805.68		$879.2069	$879.20	$879.20	$879.20