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	$83.64	8.696%	$90.9133	$90.91	$90.90	$90.90
Purchase #2	$137.71	10.245%	$151.8184	$151.82	$151.80	$151.80
Purchase #3	$93.37	9.232%	$101.9899	$101.99	$102.00	$102.00
Purchase #4	$156.31	7.357%	$167.8097	$167.81	$167.80	$167.80
Purchase #5	$57.45	4.199%	$59.8623	$59.86	$59.85	$59.90
Purchase #6	$43.69	8.178%	$47.263	$47.26	$47.25	$47.30
Purchase #7	$21.28	3.259%	$21.9735	$21.97	$21.95	$22.00
7 purchase totals =	$593.45		$641.6301	$641.62	$641.55	$641.70