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	$67.57	6.105%	$71.6951	$71.70	$71.70	$71.70
Purchase #2	$107.67	10.314%	$118.7751	$118.78	$118.80	$118.80
Purchase #3	$50.53	12.214%	$56.7017	$56.70	$56.70	$56.70
Purchase #4	$170.65	5.826%	$180.5921	$180.59	$180.60	$180.60
Purchase #5	$50.28	6.358%	$53.4768	$53.48	$53.50	$53.50
Purchase #6	$56.64	4.240%	$59.0415	$59.04	$59.05	$59.00
Purchase #7	$55.44	12.829%	$62.5524	$62.55	$62.55	$62.60
7 purchase totals =	$558.78		$602.8347	$602.84	$602.90	$602.90