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	$91.85	13.302%	$104.0679	$104.07	$104.05	$104.10
Purchase #2	$214.91	3.718%	$222.9004	$222.90	$222.90	$222.90
Purchase #3	$113.47	11.594%	$126.6257	$126.63	$126.65	$126.60
Purchase #4	$117.57	3.582%	$121.7814	$121.78	$121.80	$121.80
Purchase #5	$228.55	6.302%	$242.9532	$242.95	$242.95	$243.00
Purchase #6	$152.70	9.206%	$166.7576	$166.76	$166.75	$166.80
Purchase #7	$103.27	11.866%	$115.524	$115.52	$115.50	$115.50
7 purchase totals =	$1,022.32		$1,100.6102	$1,100.61	$1,100.60	$1,100.70