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	$86.72	4.856%	$90.9311	$90.93	$90.95	$90.90
Purchase #2	$83.31	9.649%	$91.3486	$91.35	$91.35	$91.30
Purchase #3	$90.86	9.537%	$99.5253	$99.53	$99.55	$99.50
Purchase #4	$93.74	13.262%	$106.1718	$106.17	$106.15	$106.20
Purchase #5	$101.74	7.305%	$109.1721	$109.17	$109.15	$109.20
Purchase #6	$15.88	12.333%	$17.8385	$17.84	$17.85	$17.80
Purchase #7	$108.27	7.162%	$116.0243	$116.02	$116.00	$116.00
7 purchase totals =	$580.52		$631.0117	$631.01	$631.00	$630.90