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	$124.94	6.279%	$132.785	$132.79	$132.80	$132.80
Purchase #2	$184.45	3.491%	$190.8891	$190.89	$190.90	$190.90
Purchase #3	$173.36	8.730%	$188.4943	$188.49	$188.50	$188.50
Purchase #4	$131.65	4.320%	$137.3373	$137.34	$137.35	$137.30
Purchase #5	$162.32	10.679%	$179.6542	$179.65	$179.65	$179.70
Purchase #6	$123.89	11.493%	$138.1287	$138.13	$138.15	$138.10
Purchase #7	$114.87	3.654%	$119.0673	$119.07	$119.05	$119.10
7 purchase totals =	$1,015.48		$1,086.3559	$1,086.36	$1,086.40	$1,086.40