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	$19.87	3.580%	$20.5813	$20.58	$20.60	$20.60
Purchase #2	$149.82	4.318%	$156.2892	$156.29	$156.30	$156.30
Purchase #3	$101.67	13.448%	$115.3426	$115.34	$115.35	$115.30
Purchase #4	$75.59	4.439%	$78.9454	$78.95	$78.95	$78.90
Purchase #5	$250.83	10.364%	$276.826	$276.83	$276.85	$276.80
Purchase #6	$140.53	3.130%	$144.9286	$144.93	$144.95	$144.90
Purchase #7	$243.46	11.667%	$271.8645	$271.86	$271.85	$271.90
7 purchase totals =	$981.77		$1,064.7776	$1,064.78	$1,064.85	$1,064.70