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	$156.35	10.221%	$172.3305	$172.33	$172.35	$172.30
Purchase #2	$153.40	8.368%	$166.2365	$166.24	$166.25	$166.20
Purchase #3	$237.48	11.534%	$264.8709	$264.87	$264.85	$264.90
Purchase #4	$44.84	9.132%	$48.9348	$48.93	$48.95	$48.90
Purchase #5	$87.90	13.579%	$99.8359	$99.84	$99.85	$99.80
Purchase #6	$218.54	10.252%	$240.9447	$240.94	$240.95	$240.90
Purchase #7	$44.86	9.500%	$49.1217	$49.12	$49.10	$49.10
7 purchase totals =	$943.37		$1,042.2750	$1,042.27	$1,042.30	$1,042.10