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	$123.68	13.812%	$140.7627	$140.76	$140.75	$140.80
Purchase #2	$239.87	10.161%	$264.2432	$264.24	$264.25	$264.20
Purchase #3	$59.77	9.766%	$65.6071	$65.61	$65.60	$65.60
Purchase #4	$23.48	10.333%	$25.9062	$25.91	$25.90	$25.90
Purchase #5	$106.96	11.134%	$118.8689	$118.87	$118.85	$118.90
Purchase #6	$141.39	13.691%	$160.7477	$160.75	$160.75	$160.70
Purchase #7	$210.57	6.335%	$223.9096	$223.91	$223.90	$223.90
7 purchase totals =	$905.72		$1,000.0454	$1,000.05	$1,000.00	$1,000.00