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	$203.67	12.846%	$229.8334	$229.83	$229.85	$229.80
Purchase #2	$151.94	4.177%	$158.2865	$158.29	$158.30	$158.30
Purchase #3	$122.89	9.303%	$134.3225	$134.32	$134.30	$134.30
Purchase #4	$239.95	13.793%	$273.0463	$273.05	$273.05	$273.00
Purchase #5	$65.27	3.230%	$67.3782	$67.38	$67.40	$67.40
Purchase #6	$239.90	11.667%	$267.8891	$267.89	$267.90	$267.90
Purchase #7	$195.28	13.775%	$222.1798	$222.18	$222.20	$222.20
7 purchase totals =	$1,218.90		$1,352.9358	$1,352.94	$1,353.00	$1,352.90