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	$20.30	3.203%	$20.9502	$20.95	$20.95	$21.00
Purchase #2	$43.96	3.696%	$45.5848	$45.58	$45.60	$45.60
Purchase #3	$224.83	4.489%	$234.9226	$234.92	$234.90	$234.90
Purchase #4	$172.43	4.367%	$179.96	$179.96	$179.95	$180.00
Purchase #5	$45.52	6.372%	$48.4205	$48.42	$48.40	$48.40
Purchase #6	$217.39	6.812%	$232.1986	$232.20	$232.20	$232.20
Purchase #7	$153.86	9.440%	$168.3844	$168.38	$168.40	$168.40
7 purchase totals =	$878.29		$930.4211	$930.41	$930.40	$930.50