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	$53.38	9.566%	$58.4863	$58.49	$58.50	$58.50
Purchase #2	$69.37	13.591%	$78.7981	$78.80	$78.80	$78.80
Purchase #3	$144.88	7.290%	$155.4418	$155.44	$155.45	$155.40
Purchase #4	$199.58	10.658%	$220.8512	$220.85	$220.85	$220.90
Purchase #5	$250.45	4.454%	$261.605	$261.61	$261.60	$261.60
Purchase #6	$143.36	9.211%	$156.5649	$156.56	$156.55	$156.60
Purchase #7	$150.75	5.171%	$158.5453	$158.55	$158.55	$158.50
7 purchase totals =	$1,011.77		$1,090.2926	$1,090.30	$1,090.30	$1,090.30