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	$224.54	6.238%	$238.5468	$238.55	$238.55	$238.50
Purchase #2	$155.37	13.834%	$176.8639	$176.86	$176.85	$176.90
Purchase #3	$146.70	9.219%	$160.2243	$160.22	$160.20	$160.20
Purchase #4	$130.64	5.651%	$138.0225	$138.02	$138.00	$138.00
Purchase #5	$237.93	7.405%	$255.5487	$255.55	$255.55	$255.50
Purchase #6	$84.87	6.136%	$90.0776	$90.08	$90.10	$90.10
Purchase #7	$54.72	6.517%	$58.2861	$58.29	$58.30	$58.30
7 purchase totals =	$1,034.77		$1,117.5699	$1,117.57	$1,117.55	$1,117.50