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	$18.34	9.116%	$20.0119	$20.01	$20.00	$20.00
Purchase #2	$29.69	7.426%	$31.8948	$31.89	$31.90	$31.90
Purchase #3	$26.74	10.469%	$29.5394	$29.54	$29.55	$29.50
Purchase #4	$58.78	12.721%	$66.2574	$66.26	$66.25	$66.30
Purchase #5	$183.42	13.844%	$208.8127	$208.81	$208.80	$208.80
Purchase #6	$61.92	5.863%	$65.5504	$65.55	$65.55	$65.60
Purchase #7	$6.63	13.143%	$7.5014	$7.50	$7.50	$7.50
7 purchase totals =	$385.52		$429.5680	$429.56	$429.55	$429.60