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	$211.39	5.798%	$223.6464	$223.65	$223.65	$223.60
Purchase #2	$148.88	7.416%	$159.9209	$159.92	$159.90	$159.90
Purchase #3	$51.98	10.711%	$57.5476	$57.55	$57.55	$57.50
Purchase #4	$36.80	5.426%	$38.7968	$38.80	$38.80	$38.80
Purchase #5	$186.85	5.140%	$196.4541	$196.45	$196.45	$196.50
Purchase #6	$36.48	9.857%	$40.0758	$40.08	$40.10	$40.10
Purchase #7	$33.94	9.688%	$37.2281	$37.23	$37.25	$37.20
7 purchase totals =	$706.32		$753.6697	$753.68	$753.70	$753.60