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	$40.86	7.311%	$43.8473	$43.85	$43.85	$43.80
Purchase #2	$10.44	3.806%	$10.8373	$10.84	$10.85	$10.80
Purchase #3	$134.34	6.513%	$143.0896	$143.09	$143.10	$143.10
Purchase #4	$48.90	6.183%	$51.9235	$51.92	$51.90	$51.90
Purchase #5	$218.69	4.663%	$228.8875	$228.89	$228.90	$228.90
Purchase #6	$40.38	5.258%	$42.5032	$42.50	$42.50	$42.50
Purchase #7	$140.90	12.509%	$158.5252	$158.53	$158.55	$158.50
7 purchase totals =	$634.51		$679.6136	$679.62	$679.65	$679.50