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	$203.77	12.593%	$229.4308	$229.43	$229.45	$229.40
Purchase #2	$60.51	9.409%	$66.2034	$66.20	$66.20	$66.20
Purchase #3	$42.93	11.550%	$47.8884	$47.89	$47.90	$47.90
Purchase #4	$130.90	6.602%	$139.542	$139.54	$139.55	$139.50
Purchase #5	$132.68	13.506%	$150.5998	$150.60	$150.60	$150.60
Purchase #6	$180.41	6.360%	$191.8841	$191.88	$191.90	$191.90
Purchase #7	$12.31	5.518%	$12.9893	$12.99	$13.00	$13.00
7 purchase totals =	$763.51		$838.5378	$838.53	$838.60	$838.50