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	$43.63	4.847%	$45.7447	$45.74	$45.75	$45.70
Purchase #2	$34.67	11.173%	$38.5437	$38.54	$38.55	$38.50
Purchase #3	$181.29	12.228%	$203.4581	$203.46	$203.45	$203.50
Purchase #4	$59.48	13.765%	$67.6674	$67.67	$67.65	$67.70
Purchase #5	$70.79	13.644%	$80.4486	$80.45	$80.45	$80.40
Purchase #6	$214.82	9.508%	$235.2451	$235.25	$235.25	$235.20
Purchase #7	$220.66	5.830%	$233.5245	$233.52	$233.50	$233.50
7 purchase totals =	$825.34		$904.6321	$904.63	$904.60	$904.50