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	$40.92	6.440%	$43.5552	$43.56	$43.55	$43.60
Purchase #2	$116.71	5.862%	$123.5515	$123.55	$123.55	$123.60
Purchase #3	$80.94	10.641%	$89.5528	$89.55	$89.55	$89.60
Purchase #4	$57.78	8.840%	$62.8878	$62.89	$62.90	$62.90
Purchase #5	$121.95	11.764%	$136.2962	$136.30	$136.30	$136.30
Purchase #6	$130.27	10.305%	$143.6943	$143.69	$143.70	$143.70
Purchase #7	$7.92	5.655%	$8.3679	$8.37	$8.35	$8.40
7 purchase totals =	$556.49		$607.9057	$607.91	$607.90	$608.10