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	$107.42	11.781%	$120.0752	$120.08	$120.10	$120.10
Purchase #2	$205.39	6.467%	$218.6726	$218.67	$218.65	$218.70
Purchase #3	$201.40	13.449%	$228.4863	$228.49	$228.50	$228.50
Purchase #4	$150.47	12.222%	$168.8604	$168.86	$168.85	$168.90
Purchase #5	$214.67	6.430%	$228.4733	$228.47	$228.45	$228.50
Purchase #6	$192.63	10.673%	$213.1894	$213.19	$213.20	$213.20
Purchase #7	$72.76	7.366%	$78.1195	$78.12	$78.10	$78.10
7 purchase totals =	$1,144.74		$1,255.8767	$1,255.88	$1,255.85	$1,256.00