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	$70.52	4.714%	$73.8443	$73.84	$73.85	$73.80
Purchase #2	$62.71	5.590%	$66.2155	$66.22	$66.20	$66.20
Purchase #3	$50.67	10.238%	$55.8576	$55.86	$55.85	$55.90
Purchase #4	$152.59	3.165%	$157.4195	$157.42	$157.40	$157.40
Purchase #5	$177.38	3.299%	$183.2318	$183.23	$183.25	$183.20
Purchase #6	$86.43	4.729%	$90.5173	$90.52	$90.50	$90.50
Purchase #7	$39.51	11.387%	$44.009	$44.01	$44.00	$44.00
7 purchase totals =	$639.81		$671.0950	$671.10	$671.05	$671.00