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	$24.64	3.550%	$25.5147	$25.51	$25.50	$25.50
Purchase #2	$245.40	8.152%	$265.405	$265.41	$265.40	$265.40
Purchase #3	$28.35	5.739%	$29.977	$29.98	$30.00	$30.00
Purchase #4	$53.83	11.365%	$59.9478	$59.95	$59.95	$59.90
Purchase #5	$100.37	11.409%	$111.8212	$111.82	$111.80	$111.80
Purchase #6	$147.27	12.632%	$165.8731	$165.87	$165.85	$165.90
Purchase #7	$17.90	5.255%	$18.8406	$18.84	$18.85	$18.80
7 purchase totals =	$617.76		$677.3794	$677.38	$677.35	$677.30