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	$236.81	13.386%	$268.5094	$268.51	$268.50	$268.50
Purchase #2	$62.90	8.111%	$68.0018	$68.00	$68.00	$68.00
Purchase #3	$161.58	3.632%	$167.4486	$167.45	$167.45	$167.40
Purchase #4	$72.48	12.597%	$81.6103	$81.61	$81.60	$81.60
Purchase #5	$235.43	5.294%	$247.8937	$247.89	$247.90	$247.90
Purchase #6	$55.49	12.612%	$62.4884	$62.49	$62.50	$62.50
Purchase #7	$32.88	3.181%	$33.9259	$33.93	$33.95	$33.90
7 purchase totals =	$857.57		$929.8781	$929.88	$929.90	$929.80