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	$123.89	10.124%	$136.4326	$136.43	$136.45	$136.40
Purchase #2	$156.27	9.711%	$171.4454	$171.45	$171.45	$171.40
Purchase #3	$151.98	5.529%	$160.383	$160.38	$160.40	$160.40
Purchase #4	$120.27	9.734%	$131.9771	$131.98	$132.00	$132.00
Purchase #5	$98.42	4.328%	$102.6796	$102.68	$102.70	$102.70
Purchase #6	$73.30	9.225%	$80.0619	$80.06	$80.05	$80.10
Purchase #7	$100.75	3.640%	$104.4173	$104.42	$104.40	$104.40
7 purchase totals =	$824.88		$887.3969	$887.40	$887.45	$887.40