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	$240.32	13.305%	$272.2946	$272.29	$272.30	$272.30
Purchase #2	$225.72	13.676%	$256.5895	$256.59	$256.60	$256.60
Purchase #3	$16.40	12.316%	$18.4198	$18.42	$18.40	$18.40
Purchase #4	$133.43	10.177%	$147.0092	$147.01	$147.00	$147.00
Purchase #5	$46.76	10.506%	$51.6726	$51.67	$51.65	$51.70
Purchase #6	$109.67	8.412%	$118.8954	$118.90	$118.90	$118.90
Purchase #7	$129.43	10.735%	$143.3243	$143.32	$143.30	$143.30
7 purchase totals =	$901.73		$1,008.2054	$1,008.20	$1,008.15	$1,008.20