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	$59.86	3.687%	$62.067	$62.07	$62.05	$62.10
Purchase #2	$73.81	6.410%	$78.5412	$78.54	$78.55	$78.50
Purchase #3	$66.46	12.765%	$74.9436	$74.94	$74.95	$74.90
Purchase #4	$136.79	4.761%	$143.3026	$143.30	$143.30	$143.30
Purchase #5	$247.50	4.833%	$259.4617	$259.46	$259.45	$259.50
Purchase #6	$129.90	11.261%	$144.528	$144.53	$144.55	$144.50
Purchase #7	$59.78	8.505%	$64.8643	$64.86	$64.85	$64.90
7 purchase totals =	$774.10		$827.7084	$827.70	$827.70	$827.70