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	$123.81	6.285%	$131.5915	$131.59	$131.60	$131.60
Purchase #2	$16.94	6.656%	$18.0675	$18.07	$18.05	$18.10
Purchase #3	$193.77	10.124%	$213.3873	$213.39	$213.40	$213.40
Purchase #4	$179.44	9.262%	$196.0597	$196.06	$196.05	$196.10
Purchase #5	$44.31	12.639%	$49.9103	$49.91	$49.90	$49.90
Purchase #6	$149.65	5.621%	$158.0618	$158.06	$158.05	$158.10
Purchase #7	$236.45	5.533%	$249.5328	$249.53	$249.55	$249.50
7 purchase totals =	$944.37		$1,016.6109	$1,016.61	$1,016.60	$1,016.70