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	$19.28	4.583%	$20.1636	$20.16	$20.15	$20.20
Purchase #2	$238.64	10.871%	$264.5826	$264.58	$264.60	$264.60
Purchase #3	$189.97	3.372%	$196.3758	$196.38	$196.40	$196.40
Purchase #4	$54.71	11.599%	$61.0558	$61.06	$61.05	$61.10
Purchase #5	$60.34	13.770%	$68.6488	$68.65	$68.65	$68.60
Purchase #6	$90.86	11.457%	$101.2698	$101.27	$101.25	$101.30
Purchase #7	$139.99	5.759%	$148.052	$148.05	$148.05	$148.10
7 purchase totals =	$793.79		$860.1484	$860.15	$860.15	$860.30