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	$196.83	13.610%	$223.6186	$223.62	$223.60	$223.60
Purchase #2	$109.73	8.359%	$118.9023	$118.90	$118.90	$118.90
Purchase #3	$203.48	5.586%	$214.8464	$214.85	$214.85	$214.80
Purchase #4	$127.93	11.872%	$143.1178	$143.12	$143.10	$143.10
Purchase #5	$27.51	12.274%	$30.8866	$30.89	$30.90	$30.90
Purchase #6	$101.97	12.718%	$114.9385	$114.94	$114.95	$114.90
Purchase #7	$23.72	3.639%	$24.5832	$24.58	$24.60	$24.60
7 purchase totals =	$791.17		$870.8934	$870.90	$870.90	$870.80