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	$222.87	12.215%	$250.0936	$250.09	$250.10	$250.10
Purchase #2	$243.71	12.351%	$273.8106	$273.81	$273.80	$273.80
Purchase #3	$62.84	6.549%	$66.9554	$66.96	$66.95	$67.00
Purchase #4	$222.51	11.622%	$248.3701	$248.37	$248.35	$248.40
Purchase #5	$51.25	7.605%	$55.1476	$55.15	$55.15	$55.10
Purchase #6	$120.26	4.459%	$125.6224	$125.62	$125.60	$125.60
Purchase #7	$246.56	13.772%	$280.5162	$280.52	$280.50	$280.50
7 purchase totals =	$1,170.00		$1,300.5159	$1,300.52	$1,300.45	$1,300.50