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	$32.96	13.871%	$37.5319	$37.53	$37.55	$37.50
Purchase #2	$130.28	12.769%	$146.9155	$146.92	$146.90	$146.90
Purchase #3	$162.52	13.193%	$183.9613	$183.96	$183.95	$184.00
Purchase #4	$158.39	11.167%	$176.0774	$176.08	$176.10	$176.10
Purchase #5	$89.42	11.738%	$99.9161	$99.92	$99.90	$99.90
Purchase #6	$216.78	3.706%	$224.8139	$224.81	$224.80	$224.80
Purchase #7	$136.90	10.235%	$150.9117	$150.91	$150.90	$150.90
7 purchase totals =	$927.25		$1,020.1278	$1,020.13	$1,020.10	$1,020.10