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	$37.48	6.629%	$39.9645	$39.96	$39.95	$40.00
Purchase #2	$6.61	12.624%	$7.4444	$7.44	$7.45	$7.40
Purchase #3	$241.46	3.464%	$249.8242	$249.82	$249.80	$249.80
Purchase #4	$59.90	9.373%	$65.5144	$65.51	$65.50	$65.50
Purchase #5	$142.85	10.769%	$158.2335	$158.23	$158.25	$158.20
Purchase #6	$151.51	11.762%	$169.3306	$169.33	$169.35	$169.30
Purchase #7	$186.51	5.800%	$197.3276	$197.33	$197.35	$197.30
7 purchase totals =	$826.32		$887.6392	$887.62	$887.65	$887.50