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	$147.36	6.233%	$156.5449	$156.54	$156.55	$156.50
Purchase #2	$74.35	7.621%	$80.0162	$80.02	$80.00	$80.00
Purchase #3	$179.32	11.869%	$200.6035	$200.60	$200.60	$200.60
Purchase #4	$99.37	6.487%	$105.8161	$105.82	$105.80	$105.80
Purchase #5	$78.68	6.114%	$83.4905	$83.49	$83.50	$83.50
Purchase #6	$178.49	4.356%	$186.265	$186.27	$186.25	$186.30
Purchase #7	$108.86	10.184%	$119.9463	$119.95	$119.95	$119.90
7 purchase totals =	$866.43		$932.6825	$932.69	$932.65	$932.60