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	$22.85	13.387%	$25.9089	$25.91	$25.90	$25.90
Purchase #2	$51.46	8.762%	$55.9689	$55.97	$55.95	$56.00
Purchase #3	$58.71	13.338%	$66.5407	$66.54	$66.55	$66.50
Purchase #4	$202.95	4.368%	$211.8149	$211.81	$211.80	$211.80
Purchase #5	$73.46	7.394%	$78.8916	$78.89	$78.90	$78.90
Purchase #6	$56.63	6.290%	$60.192	$60.19	$60.20	$60.20
Purchase #7	$134.70	4.310%	$140.5056	$140.51	$140.50	$140.50
7 purchase totals =	$600.76		$639.8226	$639.82	$639.80	$639.80