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	$123.41	6.634%	$131.597	$131.60	$131.60	$131.60
Purchase #2	$197.58	12.795%	$222.8604	$222.86	$222.85	$222.90
Purchase #3	$205.49	5.834%	$217.4783	$217.48	$217.50	$217.50
Purchase #4	$88.76	5.416%	$93.5672	$93.57	$93.55	$93.60
Purchase #5	$134.73	12.509%	$151.5834	$151.58	$151.60	$151.60
Purchase #6	$222.53	3.338%	$229.9581	$229.96	$229.95	$230.00
Purchase #7	$137.34	4.323%	$143.2772	$143.28	$143.30	$143.30
7 purchase totals =	$1,109.84		$1,190.3216	$1,190.33	$1,190.35	$1,190.50