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	$28.66	11.286%	$31.8946	$31.89	$31.90	$31.90
Purchase #2	$214.52	3.376%	$221.7622	$221.76	$221.75	$221.80
Purchase #3	$42.46	4.773%	$44.4866	$44.49	$44.50	$44.50
Purchase #4	$39.92	9.773%	$43.8214	$43.82	$43.80	$43.80
Purchase #5	$97.78	12.823%	$110.3183	$110.32	$110.30	$110.30
Purchase #6	$78.54	13.116%	$88.8413	$88.84	$88.85	$88.80
Purchase #7	$44.43	4.372%	$46.3725	$46.37	$46.35	$46.40
7 purchase totals =	$546.31		$587.4969	$587.49	$587.45	$587.50