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	$6.51	13.534%	$7.3911	$7.39	$7.40	$7.40
Purchase #2	$153.81	11.409%	$171.3582	$171.36	$171.35	$171.40
Purchase #3	$24.64	9.128%	$26.8891	$26.89	$26.90	$26.90
Purchase #4	$211.25	4.829%	$221.4513	$221.45	$221.45	$221.50
Purchase #5	$140.57	13.851%	$160.0404	$160.04	$160.05	$160.00
Purchase #6	$54.99	8.422%	$59.6213	$59.62	$59.60	$59.60
Purchase #7	$140.84	9.766%	$154.5944	$154.59	$154.60	$154.60
7 purchase totals =	$732.61		$801.3458	$801.34	$801.35	$801.40