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	$15.97	10.160%	$17.5926	$17.59	$17.60	$17.60
Purchase #2	$82.51	6.276%	$87.6883	$87.69	$87.70	$87.70
Purchase #3	$226.66	11.738%	$253.2654	$253.27	$253.25	$253.30
Purchase #4	$198.93	7.484%	$213.8179	$213.82	$213.80	$213.80
Purchase #5	$165.46	4.759%	$173.3342	$173.33	$173.35	$173.30
Purchase #6	$151.93	13.802%	$172.8994	$172.90	$172.90	$172.90
Purchase #7	$173.29	5.243%	$182.3756	$182.38	$182.40	$182.40
7 purchase totals =	$1,014.75		$1,100.9734	$1,100.98	$1,101.00	$1,101.00