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	$124.32	5.851%	$131.594	$131.59	$131.60	$131.60
Purchase #2	$239.97	6.853%	$256.4151	$256.42	$256.40	$256.40
Purchase #3	$82.34	8.360%	$89.2236	$89.22	$89.20	$89.20
Purchase #4	$204.63	7.817%	$220.6259	$220.63	$220.65	$220.60
Purchase #5	$205.61	4.699%	$215.2716	$215.27	$215.25	$215.30
Purchase #6	$158.35	9.606%	$173.5611	$173.56	$173.55	$173.60
Purchase #7	$142.38	9.584%	$156.0257	$156.03	$156.05	$156.00
7 purchase totals =	$1,157.60		$1,242.7170	$1,242.72	$1,242.70	$1,242.70