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	$66.91	13.348%	$75.8411	$75.84	$75.85	$75.80
Purchase #2	$42.52	3.393%	$43.9627	$43.96	$43.95	$44.00
Purchase #3	$33.31	13.712%	$37.8775	$37.88	$37.90	$37.90
Purchase #4	$96.92	7.770%	$104.4507	$104.45	$104.45	$104.50
Purchase #5	$40.92	10.762%	$45.3238	$45.32	$45.30	$45.30
Purchase #6	$230.80	6.212%	$245.1373	$245.14	$245.15	$245.10
Purchase #7	$70.34	11.298%	$78.287	$78.29	$78.30	$78.30
7 purchase totals =	$581.72		$630.8801	$630.88	$630.90	$630.90