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	$36.80	9.314%	$40.2276	$40.23	$40.25	$40.20
Purchase #2	$196.64	13.229%	$222.6535	$222.65	$222.65	$222.70
Purchase #3	$176.45	5.759%	$186.6118	$186.61	$186.60	$186.60
Purchase #4	$235.46	7.780%	$253.7788	$253.78	$253.80	$253.80
Purchase #5	$196.87	4.871%	$206.4595	$206.46	$206.45	$206.50
Purchase #6	$5.40	7.767%	$5.8194	$5.82	$5.80	$5.80
Purchase #7	$249.42	10.545%	$275.7213	$275.72	$275.70	$275.70
7 purchase totals =	$1,097.04		$1,191.2719	$1,191.27	$1,191.25	$1,191.30