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	$243.86	12.450%	$274.2206	$274.22	$274.20	$274.20
Purchase #2	$170.26	8.479%	$184.6963	$184.70	$184.70	$184.70
Purchase #3	$189.31	13.771%	$215.3799	$215.38	$215.40	$215.40
Purchase #4	$132.69	3.709%	$137.6115	$137.61	$137.60	$137.60
Purchase #5	$178.52	10.167%	$196.6701	$196.67	$196.65	$196.70
Purchase #6	$177.56	12.349%	$199.4869	$199.49	$199.50	$199.50
Purchase #7	$113.33	13.630%	$128.7769	$128.78	$128.80	$128.80
7 purchase totals =	$1,205.53		$1,336.8422	$1,336.85	$1,336.85	$1,336.90