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	$16.86	9.788%	$18.5103	$18.51	$18.50	$18.50
Purchase #2	$197.33	12.463%	$221.9232	$221.92	$221.90	$221.90
Purchase #3	$239.95	10.252%	$264.5497	$264.55	$264.55	$264.50
Purchase #4	$79.94	3.379%	$82.6412	$82.64	$82.65	$82.60
Purchase #5	$113.46	11.848%	$126.9027	$126.90	$126.90	$126.90
Purchase #6	$164.56	3.237%	$169.8868	$169.89	$169.90	$169.90
Purchase #7	$68.33	3.144%	$70.4783	$70.48	$70.50	$70.50
7 purchase totals =	$880.43		$954.8922	$954.89	$954.90	$954.80