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	$17.38	11.254%	$19.3359	$19.34	$19.35	$19.30
Purchase #2	$179.50	3.358%	$185.5276	$185.53	$185.55	$185.50
Purchase #3	$118.38	6.842%	$126.4796	$126.48	$126.50	$126.50
Purchase #4	$242.99	5.575%	$256.5367	$256.54	$256.55	$256.50
Purchase #5	$97.45	7.276%	$104.5405	$104.54	$104.55	$104.50
Purchase #6	$151.68	8.641%	$164.7867	$164.79	$164.80	$164.80
Purchase #7	$206.78	11.174%	$229.8856	$229.89	$229.90	$229.90
7 purchase totals =	$1,014.16		$1,087.0926	$1,087.11	$1,087.20	$1,087.00