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	$57.58	5.167%	$60.5552	$60.56	$60.55	$60.60
Purchase #2	$81.83	4.545%	$85.5492	$85.55	$85.55	$85.50
Purchase #3	$249.63	6.479%	$265.8035	$265.80	$265.80	$265.80
Purchase #4	$137.98	3.484%	$142.7872	$142.79	$142.80	$142.80
Purchase #5	$40.26	8.636%	$43.7369	$43.74	$43.75	$43.70
Purchase #6	$190.45	11.550%	$212.447	$212.45	$212.45	$212.40
Purchase #7	$121.55	4.673%	$127.23	$127.23	$127.25	$127.20
7 purchase totals =	$879.28		$938.1090	$938.12	$938.15	$938.00