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	$131.49	9.138%	$143.5056	$143.51	$143.50	$143.50
Purchase #2	$37.77	5.718%	$39.9297	$39.93	$39.95	$39.90
Purchase #3	$113.87	12.326%	$127.9056	$127.91	$127.90	$127.90
Purchase #4	$124.78	9.668%	$136.8437	$136.84	$136.85	$136.80
Purchase #5	$133.55	13.467%	$151.5352	$151.54	$151.55	$151.50
Purchase #6	$18.50	13.652%	$21.0256	$21.03	$21.05	$21.00
Purchase #7	$172.74	7.797%	$186.2085	$186.21	$186.20	$186.20
7 purchase totals =	$732.70		$806.9539	$806.97	$807.00	$806.80