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	$155.42	10.355%	$171.5137	$171.51	$171.50	$171.50
Purchase #2	$133.54	9.731%	$146.5348	$146.53	$146.55	$146.50
Purchase #3	$49.25	7.640%	$53.0127	$53.01	$53.00	$53.00
Purchase #4	$111.85	9.516%	$122.4936	$122.49	$122.50	$122.50
Purchase #5	$239.46	9.243%	$261.5933	$261.59	$261.60	$261.60
Purchase #6	$5.91	9.374%	$6.464	$6.46	$6.45	$6.50
Purchase #7	$206.82	5.825%	$218.8673	$218.87	$218.85	$218.90
7 purchase totals =	$902.25		$980.4794	$980.46	$980.45	$980.50