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	$145.26	4.819%	$152.2601	$152.26	$152.25	$152.30
Purchase #2	$72.52	10.334%	$80.0142	$80.01	$80.00	$80.00
Purchase #3	$117.90	11.649%	$131.6342	$131.63	$131.65	$131.60
Purchase #4	$178.67	6.425%	$190.1495	$190.15	$190.15	$190.10
Purchase #5	$21.58	11.185%	$23.9937	$23.99	$24.00	$24.00
Purchase #6	$77.89	5.832%	$82.4325	$82.43	$82.45	$82.40
Purchase #7	$250.35	4.209%	$260.8872	$260.89	$260.90	$260.90
7 purchase totals =	$864.17		$921.3714	$921.36	$921.40	$921.30