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	$70.93	11.261%	$78.9174	$78.92	$78.90	$78.90
Purchase #2	$100.73	3.626%	$104.3825	$104.38	$104.40	$104.40
Purchase #3	$207.80	13.598%	$236.0566	$236.06	$236.05	$236.10
Purchase #4	$167.98	6.683%	$179.2061	$179.21	$179.20	$179.20
Purchase #5	$130.83	5.332%	$137.8059	$137.81	$137.80	$137.80
Purchase #6	$119.61	13.782%	$136.0947	$136.09	$136.10	$136.10
Purchase #7	$202.73	5.666%	$214.2167	$214.22	$214.20	$214.20
7 purchase totals =	$1,000.61		$1,086.6799	$1,086.69	$1,086.65	$1,086.70