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	$127.48	8.615%	$138.4624	$138.46	$138.45	$138.50
Purchase #2	$61.78	5.672%	$65.2842	$65.28	$65.30	$65.30
Purchase #3	$163.45	13.584%	$185.653	$185.65	$185.65	$185.70
Purchase #4	$105.96	7.499%	$113.9059	$113.91	$113.90	$113.90
Purchase #5	$238.44	3.389%	$246.5207	$246.52	$246.50	$246.50
Purchase #6	$144.83	8.361%	$156.9392	$156.94	$156.95	$156.90
Purchase #7	$246.78	13.692%	$280.5691	$280.57	$280.55	$280.60
7 purchase totals =	$1,088.72		$1,187.3345	$1,187.33	$1,187.30	$1,187.40