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	$171.56	6.639%	$182.9499	$182.95	$182.95	$182.90
Purchase #2	$176.65	11.439%	$196.857	$196.86	$196.85	$196.90
Purchase #3	$165.45	6.757%	$176.6295	$176.63	$176.65	$176.60
Purchase #4	$72.38	12.533%	$81.4514	$81.45	$81.45	$81.50
Purchase #5	$53.41	6.449%	$56.8544	$56.85	$56.85	$56.90
Purchase #6	$50.61	9.641%	$55.4893	$55.49	$55.50	$55.50
Purchase #7	$29.31	3.732%	$30.4038	$30.40	$30.40	$30.40
7 purchase totals =	$719.37		$780.6353	$780.63	$780.65	$780.70