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	$75.63	7.761%	$81.4996	$81.50	$81.50	$81.50
Purchase #2	$218.25	10.401%	$240.9502	$240.95	$240.95	$241.00
Purchase #3	$184.46	8.599%	$200.3217	$200.32	$200.30	$200.30
Purchase #4	$186.45	5.438%	$196.5892	$196.59	$196.60	$196.60
Purchase #5	$213.34	12.720%	$240.4768	$240.48	$240.50	$240.50
Purchase #6	$81.54	13.211%	$92.3122	$92.31	$92.30	$92.30
Purchase #7	$90.58	5.812%	$95.8445	$95.84	$95.85	$95.80
7 purchase totals =	$1,050.25		$1,147.9942	$1,147.99	$1,148.00	$1,148.00