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	$236.88	8.104%	$256.0768	$256.08	$256.10	$256.10
Purchase #2	$19.71	6.250%	$20.9419	$20.94	$20.95	$20.90
Purchase #3	$97.31	5.846%	$102.9987	$103.00	$103.00	$103.00
Purchase #4	$105.81	6.240%	$112.4125	$112.41	$112.40	$112.40
Purchase #5	$217.84	4.386%	$227.3945	$227.39	$227.40	$227.40
Purchase #6	$38.33	13.240%	$43.4049	$43.40	$43.40	$43.40
Purchase #7	$53.57	9.408%	$58.6099	$58.61	$58.60	$58.60
7 purchase totals =	$769.45		$821.8392	$821.83	$821.85	$821.80