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	$29.45	8.217%	$31.8699	$31.87	$31.85	$31.90
Purchase #2	$153.36	7.508%	$164.8743	$164.87	$164.85	$164.90
Purchase #3	$64.62	9.207%	$70.5696	$70.57	$70.55	$70.60
Purchase #4	$249.42	9.169%	$272.2893	$272.29	$272.30	$272.30
Purchase #5	$199.68	11.471%	$222.5853	$222.59	$222.60	$222.60
Purchase #6	$88.58	12.671%	$99.804	$99.80	$99.80	$99.80
Purchase #7	$189.70	3.447%	$196.239	$196.24	$196.25	$196.20
7 purchase totals =	$974.81		$1,058.2314	$1,058.23	$1,058.20	$1,058.30