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	$145.59	6.512%	$155.0708	$155.07	$155.05	$155.10
Purchase #2	$137.27	9.596%	$150.4424	$150.44	$150.45	$150.40
Purchase #3	$106.62	4.473%	$111.3891	$111.39	$111.40	$111.40
Purchase #4	$127.75	9.870%	$140.3589	$140.36	$140.35	$140.40
Purchase #5	$236.64	5.341%	$249.2789	$249.28	$249.30	$249.30
Purchase #6	$217.69	9.771%	$238.9605	$238.96	$238.95	$239.00
Purchase #7	$38.25	5.320%	$40.2849	$40.28	$40.30	$40.30
7 purchase totals =	$1,009.81		$1,085.7855	$1,085.78	$1,085.80	$1,085.90