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	$69.65	12.387%	$78.2775	$78.28	$78.30	$78.30
Purchase #2	$240.61	5.329%	$253.4321	$253.43	$253.45	$253.40
Purchase #3	$98.71	3.839%	$102.4995	$102.50	$102.50	$102.50
Purchase #4	$38.74	10.240%	$42.707	$42.71	$42.70	$42.70
Purchase #5	$154.74	4.798%	$162.1644	$162.16	$162.15	$162.20
Purchase #6	$205.97	3.652%	$213.492	$213.49	$213.50	$213.50
Purchase #7	$110.71	13.250%	$125.3791	$125.38	$125.40	$125.40
7 purchase totals =	$919.13		$977.9516	$977.95	$978.00	$978.00