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	$21.78	12.599%	$24.5241	$24.52	$24.50	$24.50
Purchase #2	$92.89	6.590%	$99.0115	$99.01	$99.00	$99.00
Purchase #3	$67.64	9.212%	$73.871	$73.87	$73.85	$73.90
Purchase #4	$107.89	11.564%	$120.3664	$120.37	$120.35	$120.40
Purchase #5	$65.98	8.306%	$71.4603	$71.46	$71.45	$71.50
Purchase #6	$176.54	7.670%	$190.0806	$190.08	$190.10	$190.10
Purchase #7	$16.52	10.769%	$18.299	$18.30	$18.30	$18.30
7 purchase totals =	$549.24		$597.6129	$597.61	$597.55	$597.70