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	$137.35	5.463%	$144.8534	$144.85	$144.85	$144.90
Purchase #2	$244.82	11.254%	$272.372	$272.37	$272.35	$272.40
Purchase #3	$125.40	12.870%	$141.539	$141.54	$141.55	$141.50
Purchase #4	$73.43	11.723%	$82.0382	$82.04	$82.05	$82.00
Purchase #5	$107.42	10.792%	$119.0128	$119.01	$119.00	$119.00
Purchase #6	$99.82	10.148%	$109.9497	$109.95	$109.95	$109.90
Purchase #7	$130.26	10.373%	$143.7719	$143.77	$143.75	$143.80
7 purchase totals =	$918.50		$1,013.5370	$1,013.53	$1,013.50	$1,013.50