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	$238.52	13.522%	$270.7727	$270.77	$270.75	$270.80
Purchase #2	$108.71	5.246%	$114.4129	$114.41	$114.40	$114.40
Purchase #3	$201.94	12.316%	$226.8109	$226.81	$226.80	$226.80
Purchase #4	$95.92	4.492%	$100.2287	$100.23	$100.25	$100.20
Purchase #5	$133.62	5.839%	$141.4221	$141.42	$141.40	$141.40
Purchase #6	$76.78	12.465%	$86.3506	$86.35	$86.35	$86.40
Purchase #7	$155.74	10.383%	$171.9105	$171.91	$171.90	$171.90
7 purchase totals =	$1,011.23		$1,111.9084	$1,111.90	$1,111.85	$1,111.90