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	$37.72	7.270%	$40.4622	$40.46	$40.45	$40.50
Purchase #2	$91.27	13.427%	$103.5248	$103.52	$103.50	$103.50
Purchase #3	$218.94	5.668%	$231.3495	$231.35	$231.35	$231.30
Purchase #4	$22.95	12.759%	$25.8782	$25.88	$25.90	$25.90
Purchase #5	$153.63	7.586%	$165.2844	$165.28	$165.30	$165.30
Purchase #6	$136.94	12.582%	$154.1698	$154.17	$154.15	$154.20
Purchase #7	$198.96	9.422%	$217.706	$217.71	$217.70	$217.70
7 purchase totals =	$860.41		$938.3749	$938.37	$938.35	$938.40