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	$93.54	7.517%	$100.5714	$100.57	$100.55	$100.60
Purchase #2	$166.57	13.469%	$189.0053	$189.01	$189.00	$189.00
Purchase #3	$232.98	9.705%	$255.5907	$255.59	$255.60	$255.60
Purchase #4	$213.47	5.285%	$224.7519	$224.75	$224.75	$224.80
Purchase #5	$22.32	7.296%	$23.9485	$23.95	$23.95	$23.90
Purchase #6	$230.33	12.692%	$259.5635	$259.56	$259.55	$259.60
Purchase #7	$233.30	9.528%	$255.5288	$255.53	$255.55	$255.50
7 purchase totals =	$1,192.51		$1,308.9601	$1,308.96	$1,308.95	$1,309.00