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	$154.33	5.175%	$162.3166	$162.32	$162.30	$162.30
Purchase #2	$133.50	4.838%	$139.9587	$139.96	$139.95	$140.00
Purchase #3	$32.94	10.121%	$36.2739	$36.27	$36.25	$36.30
Purchase #4	$120.86	7.635%	$130.0877	$130.09	$130.10	$130.10
Purchase #5	$244.68	12.245%	$274.6411	$274.64	$274.65	$274.60
Purchase #6	$171.88	10.804%	$190.4499	$190.45	$190.45	$190.40
Purchase #7	$27.98	3.275%	$28.8963	$28.90	$28.90	$28.90
7 purchase totals =	$886.17		$962.6242	$962.63	$962.60	$962.60