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	$154.76	7.857%	$166.9195	$166.92	$166.90	$166.90
Purchase #2	$38.34	13.661%	$43.5776	$43.58	$43.60	$43.60
Purchase #3	$168.50	4.336%	$175.8062	$175.81	$175.80	$175.80
Purchase #4	$243.59	5.339%	$256.5953	$256.60	$256.60	$256.60
Purchase #5	$40.99	13.331%	$46.4544	$46.45	$46.45	$46.50
Purchase #6	$107.97	8.267%	$116.8959	$116.90	$116.90	$116.90
Purchase #7	$167.87	9.790%	$184.3045	$184.30	$184.30	$184.30
7 purchase totals =	$922.02		$990.5534	$990.56	$990.55	$990.60