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	$160.65	4.305%	$167.566	$167.57	$167.55	$167.60
Purchase #2	$217.45	3.629%	$225.3413	$225.34	$225.35	$225.30
Purchase #3	$127.72	9.376%	$139.695	$139.70	$139.70	$139.70
Purchase #4	$131.31	13.500%	$149.0369	$149.04	$149.05	$149.00
Purchase #5	$148.63	10.595%	$164.3773	$164.38	$164.40	$164.40
Purchase #6	$39.88	7.231%	$42.7637	$42.76	$42.75	$42.80
Purchase #7	$94.27	4.818%	$98.8119	$98.81	$98.80	$98.80
7 purchase totals =	$919.91		$987.5921	$987.60	$987.60	$987.60