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	$54.93	5.380%	$57.8852	$57.89	$57.90	$57.90
Purchase #2	$236.64	6.278%	$251.4963	$251.50	$251.50	$251.50
Purchase #3	$176.89	12.163%	$198.4051	$198.41	$198.40	$198.40
Purchase #4	$228.69	13.687%	$259.9908	$259.99	$260.00	$260.00
Purchase #5	$149.72	8.611%	$162.6124	$162.61	$162.60	$162.60
Purchase #6	$157.91	10.754%	$174.8916	$174.89	$174.90	$174.90
Purchase #7	$56.67	4.525%	$59.2343	$59.23	$59.25	$59.20
7 purchase totals =	$1,061.45		$1,164.5157	$1,164.52	$1,164.55	$1,164.50