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	$143.94	11.709%	$160.7939	$160.79	$160.80	$160.80
Purchase #2	$127.95	12.128%	$143.4678	$143.47	$143.45	$143.50
Purchase #3	$217.76	10.267%	$240.1174	$240.12	$240.10	$240.10
Purchase #4	$60.68	10.674%	$67.157	$67.16	$67.15	$67.20
Purchase #5	$45.89	8.312%	$49.7044	$49.70	$49.70	$49.70
Purchase #6	$104.84	7.489%	$112.6915	$112.69	$112.70	$112.70
Purchase #7	$56.25	5.664%	$59.436	$59.44	$59.45	$59.40
7 purchase totals =	$757.31		$833.3680	$833.37	$833.35	$833.40