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	$55.47	5.162%	$58.3334	$58.33	$58.35	$58.30
Purchase #2	$207.62	13.609%	$235.875	$235.88	$235.90	$235.90
Purchase #3	$56.67	5.264%	$59.6531	$59.65	$59.65	$59.70
Purchase #4	$17.82	9.724%	$19.5528	$19.55	$19.55	$19.60
Purchase #5	$187.47	12.700%	$211.2787	$211.28	$211.30	$211.30
Purchase #6	$157.53	9.531%	$172.5442	$172.54	$172.55	$172.50
Purchase #7	$81.39	10.305%	$89.7772	$89.78	$89.80	$89.80
7 purchase totals =	$763.97		$847.0144	$847.01	$847.10	$847.10