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	$189.34	5.785%	$200.2933	$200.29	$200.30	$200.30
Purchase #2	$99.99	7.565%	$107.5542	$107.55	$107.55	$107.60
Purchase #3	$250.90	3.781%	$260.3865	$260.39	$260.40	$260.40
Purchase #4	$190.54	3.134%	$196.5115	$196.51	$196.50	$196.50
Purchase #5	$60.94	9.793%	$66.9079	$66.91	$66.90	$66.90
Purchase #6	$51.52	3.807%	$53.4814	$53.48	$53.50	$53.50
Purchase #7	$52.65	7.533%	$56.6161	$56.62	$56.60	$56.60
7 purchase totals =	$895.88		$941.7509	$941.75	$941.75	$941.80