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	$101.97	9.637%	$111.7968	$111.80	$111.80	$111.80
Purchase #2	$39.86	11.656%	$44.5061	$44.51	$44.50	$44.50
Purchase #3	$218.66	4.862%	$229.2912	$229.29	$229.30	$229.30
Purchase #4	$86.48	10.280%	$95.3701	$95.37	$95.35	$95.40
Purchase #5	$125.35	11.461%	$139.7164	$139.72	$139.70	$139.70
Purchase #6	$25.88	12.798%	$29.1921	$29.19	$29.20	$29.20
Purchase #7	$53.71	11.606%	$59.9436	$59.94	$59.95	$59.90
7 purchase totals =	$651.91		$709.8163	$709.82	$709.80	$709.80