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	$80.36	9.218%	$87.7676	$87.77	$87.75	$87.80
Purchase #2	$38.85	12.848%	$43.8414	$43.84	$43.85	$43.80
Purchase #3	$46.75	8.867%	$50.8953	$50.90	$50.90	$50.90
Purchase #4	$98.66	12.409%	$110.9027	$110.90	$110.90	$110.90
Purchase #5	$28.72	10.793%	$31.8197	$31.82	$31.80	$31.80
Purchase #6	$25.71	8.509%	$27.8977	$27.90	$27.90	$27.90
Purchase #7	$8.78	7.801%	$9.4649	$9.46	$9.45	$9.50
7 purchase totals =	$327.83		$362.5893	$362.59	$362.55	$362.60