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	$148.69	12.603%	$167.4294	$167.43	$167.45	$167.40
Purchase #2	$80.39	10.199%	$88.589	$88.59	$88.60	$88.60
Purchase #3	$80.81	10.788%	$89.5278	$89.53	$89.55	$89.50
Purchase #4	$139.47	13.428%	$158.198	$158.20	$158.20	$158.20
Purchase #5	$7.35	12.171%	$8.2446	$8.24	$8.25	$8.20
Purchase #6	$108.57	9.637%	$119.0329	$119.03	$119.05	$119.00
Purchase #7	$38.30	5.372%	$40.3575	$40.36	$40.35	$40.40
7 purchase totals =	$603.58		$671.3792	$671.38	$671.45	$671.30