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	$77.66	9.843%	$85.3041	$85.30	$85.30	$85.30
Purchase #2	$137.96	13.747%	$156.9254	$156.93	$156.95	$156.90
Purchase #3	$74.83	9.849%	$82.2	$82.20	$82.20	$82.20
Purchase #4	$71.99	4.137%	$74.9682	$74.97	$74.95	$75.00
Purchase #5	$134.40	8.299%	$145.5539	$145.55	$145.55	$145.60
Purchase #6	$70.78	11.521%	$78.9346	$78.93	$78.95	$78.90
Purchase #7	$212.65	3.719%	$220.5585	$220.56	$220.55	$220.60
7 purchase totals =	$780.27		$844.4447	$844.44	$844.45	$844.50