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	$36.27	12.328%	$40.7414	$40.74	$40.75	$40.70
Purchase #2	$238.27	10.238%	$262.6641	$262.66	$262.65	$262.70
Purchase #3	$43.62	3.677%	$45.2239	$45.22	$45.20	$45.20
Purchase #4	$135.79	13.453%	$154.0578	$154.06	$154.05	$154.10
Purchase #5	$76.98	11.243%	$85.6349	$85.63	$85.65	$85.60
Purchase #6	$63.37	5.243%	$66.6925	$66.69	$66.70	$66.70
Purchase #7	$118.40	13.407%	$134.2739	$134.27	$134.25	$134.30
7 purchase totals =	$712.70		$789.2885	$789.27	$789.25	$789.30