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	$226.96	6.599%	$241.9371	$241.94	$241.95	$241.90
Purchase #2	$213.43	3.332%	$220.5415	$220.54	$220.55	$220.50
Purchase #3	$192.86	9.155%	$210.5163	$210.52	$210.50	$210.50
Purchase #4	$113.57	7.300%	$121.8606	$121.86	$121.85	$121.90
Purchase #5	$168.53	11.706%	$188.2581	$188.26	$188.25	$188.30
Purchase #6	$44.80	12.127%	$50.2329	$50.23	$50.25	$50.20
Purchase #7	$151.48	10.555%	$167.4687	$167.47	$167.45	$167.50
7 purchase totals =	$1,111.63		$1,200.8152	$1,200.82	$1,200.80	$1,200.80