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	$6.29	4.650%	$6.5825	$6.58	$6.60	$6.60
Purchase #2	$131.49	4.846%	$137.862	$137.86	$137.85	$137.90
Purchase #3	$101.75	3.579%	$105.3916	$105.39	$105.40	$105.40
Purchase #4	$202.45	10.207%	$223.1141	$223.11	$223.10	$223.10
Purchase #5	$99.59	10.228%	$109.7761	$109.78	$109.80	$109.80
Purchase #6	$66.69	3.605%	$69.0942	$69.09	$69.10	$69.10
Purchase #7	$106.26	9.497%	$116.3515	$116.35	$116.35	$116.40
7 purchase totals =	$714.52		$768.1720	$768.16	$768.20	$768.30