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	$9.90	5.456%	$10.4401	$10.44	$10.45	$10.40
Purchase #2	$87.49	13.787%	$99.5522	$99.55	$99.55	$99.60
Purchase #3	$207.57	12.786%	$234.1099	$234.11	$234.10	$234.10
Purchase #4	$207.54	4.806%	$217.5144	$217.51	$217.50	$217.50
Purchase #5	$171.85	7.800%	$185.2543	$185.25	$185.25	$185.30
Purchase #6	$163.75	11.612%	$182.7647	$182.76	$182.75	$182.80
Purchase #7	$144.40	10.762%	$159.9403	$159.94	$159.95	$159.90
7 purchase totals =	$992.50		$1,089.5759	$1,089.56	$1,089.55	$1,089.60