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	$101.46	7.807%	$109.381	$109.38	$109.40	$109.40
Purchase #2	$136.54	12.539%	$153.6608	$153.66	$153.65	$153.70
Purchase #3	$147.49	7.575%	$158.6624	$158.66	$158.65	$158.70
Purchase #4	$133.51	6.690%	$142.4418	$142.44	$142.45	$142.40
Purchase #5	$112.96	4.397%	$117.9269	$117.93	$117.95	$117.90
Purchase #6	$157.59	6.768%	$168.2557	$168.26	$168.25	$168.30
Purchase #7	$168.88	12.632%	$190.2129	$190.21	$190.20	$190.20
7 purchase totals =	$958.43		$1,040.5415	$1,040.54	$1,040.55	$1,040.60