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	$79.79	12.587%	$89.8332	$89.83	$89.85	$89.80
Purchase #2	$164.71	10.707%	$182.3455	$182.35	$182.35	$182.30
Purchase #3	$93.34	9.131%	$101.8629	$101.86	$101.85	$101.90
Purchase #4	$196.49	5.567%	$207.4286	$207.43	$207.45	$207.40
Purchase #5	$243.88	4.637%	$255.1887	$255.19	$255.20	$255.20
Purchase #6	$141.25	7.392%	$151.6912	$151.69	$151.70	$151.70
Purchase #7	$167.30	10.685%	$185.176	$185.18	$185.20	$185.20
7 purchase totals =	$1,086.76		$1,173.5261	$1,173.53	$1,173.60	$1,173.50