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	$215.48	7.389%	$231.4018	$231.40	$231.40	$231.40
Purchase #2	$90.85	13.409%	$103.0321	$103.03	$103.05	$103.00
Purchase #3	$123.50	6.586%	$131.6337	$131.63	$131.65	$131.60
Purchase #4	$30.62	13.348%	$34.7072	$34.71	$34.70	$34.70
Purchase #5	$219.52	8.747%	$238.7214	$238.72	$238.70	$238.70
Purchase #6	$54.32	6.219%	$57.6982	$57.70	$57.70	$57.70
Purchase #7	$37.55	7.776%	$40.4699	$40.47	$40.45	$40.50
7 purchase totals =	$771.84		$837.6643	$837.66	$837.65	$837.60