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	$27.82	5.303%	$29.2953	$29.30	$29.30	$29.30
Purchase #2	$109.61	13.580%	$124.495	$124.50	$124.50	$124.50
Purchase #3	$61.60	7.573%	$66.265	$66.27	$66.25	$66.30
Purchase #4	$111.40	7.267%	$119.4954	$119.50	$119.50	$119.50
Purchase #5	$162.60	13.826%	$185.0811	$185.08	$185.10	$185.10
Purchase #6	$189.38	12.706%	$213.4426	$213.44	$213.45	$213.40
Purchase #7	$202.90	3.296%	$209.5876	$209.59	$209.60	$209.60
7 purchase totals =	$865.31		$947.6620	$947.68	$947.70	$947.70