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	$171.70	6.466%	$182.8021	$182.80	$182.80	$182.80
Purchase #2	$218.39	13.801%	$248.53	$248.53	$248.55	$248.50
Purchase #3	$43.26	10.228%	$47.6846	$47.68	$47.70	$47.70
Purchase #4	$152.68	6.565%	$162.7034	$162.70	$162.70	$162.70
Purchase #5	$18.81	12.412%	$21.1447	$21.14	$21.15	$21.10
Purchase #6	$40.78	4.378%	$42.5653	$42.57	$42.55	$42.60
Purchase #7	$100.38	10.817%	$111.2381	$111.24	$111.25	$111.20
7 purchase totals =	$746.00		$816.6682	$816.66	$816.70	$816.60