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	$124.99	13.526%	$141.8961	$141.90	$141.90	$141.90
Purchase #2	$145.54	7.790%	$156.8776	$156.88	$156.90	$156.90
Purchase #3	$144.74	13.259%	$163.9311	$163.93	$163.95	$163.90
Purchase #4	$172.32	9.298%	$188.3423	$188.34	$188.35	$188.30
Purchase #5	$107.67	3.834%	$111.7981	$111.80	$111.80	$111.80
Purchase #6	$62.80	3.458%	$64.9716	$64.97	$64.95	$65.00
Purchase #7	$230.71	10.121%	$254.0602	$254.06	$254.05	$254.10
7 purchase totals =	$988.77		$1,081.8770	$1,081.88	$1,081.90	$1,081.90