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	$225.49	12.387%	$253.4214	$253.42	$253.40	$253.40
Purchase #2	$77.96	9.603%	$85.4465	$85.45	$85.45	$85.40
Purchase #3	$100.97	4.632%	$105.6469	$105.65	$105.65	$105.60
Purchase #4	$235.89	6.230%	$250.5859	$250.59	$250.60	$250.60
Purchase #5	$123.71	3.380%	$127.8914	$127.89	$127.90	$127.90
Purchase #6	$83.27	12.247%	$93.4681	$93.47	$93.45	$93.50
Purchase #7	$56.56	4.219%	$58.9463	$58.95	$58.95	$58.90
7 purchase totals =	$903.85		$975.4065	$975.42	$975.40	$975.30