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	$227.69	12.223%	$255.5205	$255.52	$255.50	$255.50
Purchase #2	$89.78	10.514%	$99.2195	$99.22	$99.20	$99.20
Purchase #3	$38.72	3.264%	$39.9838	$39.98	$40.00	$40.00
Purchase #4	$133.44	3.605%	$138.2505	$138.25	$138.25	$138.30
Purchase #5	$198.91	10.792%	$220.3764	$220.38	$220.40	$220.40
Purchase #6	$201.57	13.238%	$228.2538	$228.25	$228.25	$228.30
Purchase #7	$66.57	7.201%	$71.3637	$71.36	$71.35	$71.40
7 purchase totals =	$956.68		$1,052.9682	$1,052.96	$1,052.95	$1,053.10