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	$201.69	9.303%	$220.4532	$220.45	$220.45	$220.50
Purchase #2	$51.76	7.816%	$55.8056	$55.81	$55.80	$55.80
Purchase #3	$63.42	6.734%	$67.6907	$67.69	$67.70	$67.70
Purchase #4	$157.78	6.388%	$167.859	$167.86	$167.85	$167.90
Purchase #5	$98.82	7.113%	$105.8491	$105.85	$105.85	$105.80
Purchase #6	$53.66	4.834%	$56.2539	$56.25	$56.25	$56.30
Purchase #7	$224.51	7.766%	$241.9454	$241.95	$241.95	$241.90
7 purchase totals =	$851.64		$915.8569	$915.86	$915.85	$915.90