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	$36.45	6.370%	$38.7719	$38.77	$38.75	$38.80
Purchase #2	$63.87	11.825%	$71.4226	$71.42	$71.40	$71.40
Purchase #3	$227.50	13.619%	$258.4832	$258.48	$258.50	$258.50
Purchase #4	$244.33	13.635%	$277.6444	$277.64	$277.65	$277.60
Purchase #5	$13.73	4.225%	$14.3101	$14.31	$14.30	$14.30
Purchase #6	$150.64	5.114%	$158.3437	$158.34	$158.35	$158.30
Purchase #7	$241.34	9.527%	$264.3325	$264.33	$264.35	$264.30
7 purchase totals =	$977.86		$1,083.3084	$1,083.29	$1,083.30	$1,083.20