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	$187.89	13.477%	$213.2119	$213.21	$213.20	$213.20
Purchase #2	$172.70	8.748%	$187.8078	$187.81	$187.80	$187.80
Purchase #3	$213.25	13.656%	$242.3714	$242.37	$242.35	$242.40
Purchase #4	$96.46	4.516%	$100.8161	$100.82	$100.80	$100.80
Purchase #5	$59.29	8.428%	$64.287	$64.29	$64.30	$64.30
Purchase #6	$56.77	8.469%	$61.5779	$61.58	$61.60	$61.60
Purchase #7	$124.58	9.528%	$136.45	$136.45	$136.45	$136.50
7 purchase totals =	$910.94		$1,006.5221	$1,006.53	$1,006.50	$1,006.60