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	$90.93	11.651%	$101.5243	$101.52	$101.50	$101.50
Purchase #2	$95.69	13.108%	$108.233	$108.23	$108.25	$108.20
Purchase #3	$124.25	13.184%	$140.6311	$140.63	$140.65	$140.60
Purchase #4	$53.54	4.469%	$55.9327	$55.93	$55.95	$55.90
Purchase #5	$34.59	10.789%	$38.3219	$38.32	$38.30	$38.30
Purchase #6	$102.51	3.321%	$105.9144	$105.91	$105.90	$105.90
Purchase #7	$121.63	8.252%	$131.6669	$131.67	$131.65	$131.70
7 purchase totals =	$623.14		$682.2243	$682.21	$682.20	$682.10