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	$32.68	11.410%	$36.4088	$36.41	$36.40	$36.40
Purchase #2	$75.72	9.670%	$83.0421	$83.04	$83.05	$83.00
Purchase #3	$93.74	7.235%	$100.5221	$100.52	$100.50	$100.50
Purchase #4	$183.91	10.844%	$203.8532	$203.85	$203.85	$203.90
Purchase #5	$36.80	4.710%	$38.5333	$38.53	$38.55	$38.50
Purchase #6	$22.77	8.844%	$24.7838	$24.78	$24.80	$24.80
Purchase #7	$147.43	3.337%	$152.3497	$152.35	$152.35	$152.30
7 purchase totals =	$593.05		$639.4930	$639.48	$639.50	$639.40