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	$39.99	10.819%	$44.3165	$44.32	$44.30	$44.30
Purchase #2	$222.54	8.617%	$241.7163	$241.72	$241.70	$241.70
Purchase #3	$127.48	13.760%	$145.0212	$145.02	$145.00	$145.00
Purchase #4	$104.59	11.263%	$116.37	$116.37	$116.35	$116.40
Purchase #5	$211.27	7.484%	$227.0814	$227.08	$227.10	$227.10
Purchase #6	$238.32	9.673%	$261.3727	$261.37	$261.35	$261.40
Purchase #7	$58.40	12.274%	$65.568	$65.57	$65.55	$65.60
7 purchase totals =	$1,002.59		$1,101.4461	$1,101.45	$1,101.35	$1,101.50