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	$246.72	4.278%	$257.2747	$257.27	$257.25	$257.30
Purchase #2	$139.89	13.787%	$159.1766	$159.18	$159.20	$159.20
Purchase #3	$160.98	11.734%	$179.8694	$179.87	$179.85	$179.90
Purchase #4	$171.68	12.522%	$193.1778	$193.18	$193.20	$193.20
Purchase #5	$6.78	4.771%	$7.1035	$7.10	$7.10	$7.10
Purchase #6	$174.70	12.484%	$196.5095	$196.51	$196.50	$196.50
Purchase #7	$17.41	6.252%	$18.4985	$18.50	$18.50	$18.50
7 purchase totals =	$918.16		$1,011.6100	$1,011.61	$1,011.60	$1,011.70