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	$109.68	13.570%	$124.5636	$124.56	$124.55	$124.60
Purchase #2	$145.82	11.708%	$162.8926	$162.89	$162.90	$162.90
Purchase #3	$38.31	11.201%	$42.6011	$42.60	$42.60	$42.60
Purchase #4	$112.42	9.568%	$123.1763	$123.18	$123.20	$123.20
Purchase #5	$107.95	6.829%	$115.3219	$115.32	$115.30	$115.30
Purchase #6	$112.45	9.721%	$123.3813	$123.38	$123.40	$123.40
Purchase #7	$122.60	9.787%	$134.5989	$134.60	$134.60	$134.60
7 purchase totals =	$749.23		$826.5357	$826.53	$826.55	$826.60