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	$232.89	11.752%	$260.2592	$260.26	$260.25	$260.30
Purchase #2	$164.46	9.165%	$179.5328	$179.53	$179.55	$179.50
Purchase #3	$117.34	9.808%	$128.8487	$128.85	$128.85	$128.80
Purchase #4	$98.30	7.413%	$105.587	$105.59	$105.60	$105.60
Purchase #5	$105.59	13.306%	$119.6398	$119.64	$119.65	$119.60
Purchase #6	$49.49	9.534%	$54.2084	$54.21	$54.20	$54.20
Purchase #7	$78.53	9.225%	$85.7744	$85.77	$85.75	$85.80
7 purchase totals =	$846.60		$933.8503	$933.85	$933.85	$933.80