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	$146.52	6.815%	$156.5053	$156.51	$156.50	$156.50
Purchase #2	$108.44	13.867%	$123.4774	$123.48	$123.50	$123.50
Purchase #3	$190.57	6.775%	$203.4811	$203.48	$203.50	$203.50
Purchase #4	$31.49	6.776%	$33.6238	$33.62	$33.60	$33.60
Purchase #5	$64.70	6.162%	$68.6868	$68.69	$68.70	$68.70
Purchase #6	$79.78	13.355%	$90.4346	$90.43	$90.45	$90.40
Purchase #7	$228.78	4.583%	$239.265	$239.27	$239.25	$239.30
7 purchase totals =	$850.28		$915.4740	$915.48	$915.50	$915.50