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	$38.35	10.476%	$42.3675	$42.37	$42.35	$42.40
Purchase #2	$201.61	7.810%	$217.3557	$217.36	$217.35	$217.40
Purchase #3	$75.53	6.258%	$80.2567	$80.26	$80.25	$80.30
Purchase #4	$196.76	9.160%	$214.7832	$214.78	$214.80	$214.80
Purchase #5	$203.95	8.582%	$221.453	$221.45	$221.45	$221.50
Purchase #6	$244.70	4.319%	$255.2686	$255.27	$255.25	$255.30
Purchase #7	$178.31	4.195%	$185.7901	$185.79	$185.80	$185.80
7 purchase totals =	$1,139.21		$1,217.2748	$1,217.28	$1,217.25	$1,217.50