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	$139.33	12.238%	$156.3812	$156.38	$156.40	$156.40
Purchase #2	$190.90	11.748%	$213.3269	$213.33	$213.35	$213.30
Purchase #3	$76.45	13.447%	$86.7302	$86.73	$86.75	$86.70
Purchase #4	$158.56	5.617%	$167.4663	$167.47	$167.45	$167.50
Purchase #5	$7.38	4.513%	$7.7131	$7.71	$7.70	$7.70
Purchase #6	$79.25	13.826%	$90.2071	$90.21	$90.20	$90.20
Purchase #7	$28.92	9.389%	$31.6353	$31.64	$31.65	$31.60
7 purchase totals =	$680.79		$753.4601	$753.47	$753.50	$753.40