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	$38.98	11.384%	$43.4175	$43.42	$43.40	$43.40
Purchase #2	$32.83	10.277%	$36.2039	$36.20	$36.20	$36.20
Purchase #3	$125.96	13.185%	$142.5678	$142.57	$142.55	$142.60
Purchase #4	$83.47	7.160%	$89.4465	$89.45	$89.45	$89.40
Purchase #5	$44.97	12.836%	$50.7423	$50.74	$50.75	$50.70
Purchase #6	$39.93	5.806%	$42.2483	$42.25	$42.25	$42.20
Purchase #7	$47.59	11.161%	$52.9015	$52.90	$52.90	$52.90
7 purchase totals =	$413.73		$457.5278	$457.53	$457.50	$457.40