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	$31.46	12.446%	$35.3755	$35.38	$35.40	$35.40
Purchase #2	$237.68	13.397%	$269.522	$269.52	$269.50	$269.50
Purchase #3	$238.59	8.399%	$258.6292	$258.63	$258.65	$258.60
Purchase #4	$72.51	9.416%	$79.3375	$79.34	$79.35	$79.30
Purchase #5	$19.88	3.552%	$20.5861	$20.59	$20.60	$20.60
Purchase #6	$142.29	11.591%	$158.7828	$158.78	$158.80	$158.80
Purchase #7	$25.49	7.732%	$27.4609	$27.46	$27.45	$27.50
7 purchase totals =	$767.90		$849.6940	$849.70	$849.75	$849.70