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	$150.52	9.837%	$165.3267	$165.33	$165.35	$165.30
Purchase #2	$91.86	12.420%	$103.269	$103.27	$103.25	$103.30
Purchase #3	$161.92	7.512%	$174.0834	$174.08	$174.10	$174.10
Purchase #4	$75.56	4.324%	$78.8272	$78.83	$78.85	$78.80
Purchase #5	$19.25	13.275%	$21.8054	$21.81	$21.80	$21.80
Purchase #6	$38.62	10.775%	$42.7813	$42.78	$42.80	$42.80
Purchase #7	$91.76	13.691%	$104.3229	$104.32	$104.30	$104.30
7 purchase totals =	$629.49		$690.4159	$690.42	$690.45	$690.40