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	$39.92	6.420%	$42.4829	$42.48	$42.50	$42.50
Purchase #2	$231.51	7.281%	$248.3662	$248.37	$248.35	$248.40
Purchase #3	$58.47	8.704%	$63.5592	$63.56	$63.55	$63.60
Purchase #4	$150.75	13.804%	$171.5595	$171.56	$171.55	$171.60
Purchase #5	$136.98	4.564%	$143.2318	$143.23	$143.25	$143.20
Purchase #6	$231.42	12.283%	$259.8453	$259.85	$259.85	$259.80
Purchase #7	$183.80	13.425%	$208.4752	$208.48	$208.50	$208.50
7 purchase totals =	$1,032.85		$1,137.5201	$1,137.53	$1,137.55	$1,137.60