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	$21.53	12.181%	$24.1526	$24.15	$24.15	$24.20
Purchase #2	$215.96	5.188%	$227.164	$227.16	$227.15	$227.20
Purchase #3	$247.29	10.730%	$273.8242	$273.82	$273.80	$273.80
Purchase #4	$11.45	7.823%	$12.3457	$12.35	$12.35	$12.30
Purchase #5	$216.48	11.483%	$241.3384	$241.34	$241.35	$241.30
Purchase #6	$72.25	3.745%	$74.9558	$74.96	$74.95	$75.00
Purchase #7	$79.42	12.538%	$89.3777	$89.38	$89.40	$89.40
7 purchase totals =	$864.38		$943.1584	$943.16	$943.15	$943.20