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	$39.98	7.262%	$42.8833	$42.88	$42.90	$42.90
Purchase #2	$244.73	5.256%	$257.593	$257.59	$257.60	$257.60
Purchase #3	$62.85	6.710%	$67.0672	$67.07	$67.05	$67.10
Purchase #4	$95.47	5.115%	$100.3533	$100.35	$100.35	$100.40
Purchase #5	$40.32	11.145%	$44.8137	$44.81	$44.80	$44.80
Purchase #6	$119.39	4.734%	$125.0419	$125.04	$125.05	$125.00
Purchase #7	$22.63	6.776%	$24.1634	$24.16	$24.15	$24.20
7 purchase totals =	$625.37		$661.9158	$661.90	$661.90	$662.00