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	$139.48	12.319%	$156.6625	$156.66	$156.65	$156.70
Purchase #2	$82.34	7.528%	$88.5386	$88.54	$88.55	$88.50
Purchase #3	$167.43	9.835%	$183.8967	$183.90	$183.90	$183.90
Purchase #4	$160.39	7.613%	$172.6005	$172.60	$172.60	$172.60
Purchase #5	$41.79	4.343%	$43.6049	$43.60	$43.60	$43.60
Purchase #6	$44.83	13.711%	$50.9766	$50.98	$51.00	$51.00
Purchase #7	$77.31	5.556%	$81.6053	$81.61	$81.60	$81.60
7 purchase totals =	$713.57		$777.8851	$777.89	$777.90	$777.90