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	$171.62	10.626%	$189.8563	$189.86	$189.85	$189.90
Purchase #2	$234.81	9.254%	$256.5393	$256.54	$256.55	$256.50
Purchase #3	$83.90	13.676%	$95.3742	$95.37	$95.35	$95.40
Purchase #4	$155.93	6.874%	$166.6486	$166.65	$166.65	$166.60
Purchase #5	$204.48	5.254%	$215.2234	$215.22	$215.20	$215.20
Purchase #6	$176.28	10.349%	$194.5232	$194.52	$194.50	$194.50
Purchase #7	$119.56	3.378%	$123.5987	$123.60	$123.60	$123.60
7 purchase totals =	$1,146.58		$1,241.7637	$1,241.76	$1,241.70	$1,241.70