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	$38.89	5.146%	$40.8913	$40.89	$40.90	$40.90
Purchase #2	$70.92	9.838%	$77.8971	$77.90	$77.90	$77.90
Purchase #3	$156.94	8.700%	$170.5938	$170.59	$170.60	$170.60
Purchase #4	$145.89	12.826%	$164.6019	$164.60	$164.60	$164.60
Purchase #5	$100.99	7.585%	$108.6501	$108.65	$108.65	$108.70
Purchase #6	$82.44	4.533%	$86.177	$86.18	$86.20	$86.20
Purchase #7	$106.27	10.723%	$117.6653	$117.67	$117.65	$117.70
7 purchase totals =	$702.34		$766.4765	$766.48	$766.50	$766.60